Traditional masculinity is a funny thing. Personally, I try not to care about it too much. I don't particularly care for sports or cars. You probably wouldn't describe me as rugged, or particularly suave. I like whiskey, but I don't wanna turn that into a personality trait, right? I'm good with computers, but that doesn't make me feel especially cool. And I'm not, like, opposed to emotions, or anything like that. And I'm mostly fine with that... But I need a little something. So I'm going to take traditional masculinity where I can get it. I was often told that I really knew how to wear a suit -- so when a couple of friends started talking to me about lapel widths and pick stitching... I was a little rattled. Suits were something that I thought accounted for my emotional, musical-loving ass, 5'6 stature, high-pitched voice, and all. So I had to do some research. I needed to learn how to talk about suits.
A few years later, after digging through mfa for way more hours than I ever thought I would, I'm in a position to make the sub what I always hoped for it to be. This guide is here to make sure that, if you find yourself in a room with Tom Ford, you don't make a fool of yourself. You'll also be able to talk to your tailor like a pro.
One more note: This guide is insanely long. Don't binge it. I don't even know why I wrote it. Nobody paid me to do this. What's wrong with me?
What is a suit?
Quick and dirty: a suit is a set of matching garments, consisting of a jacket, pants (or a skirt, or something), and optionally, a vest/waistcoat. They have to match. They have to match.
Note that I'm not talking about law suits. This is MFA. If you want to talk about litigation, and you're in New York, message me, I charge very reasonable rates.
What isn't a suit?
A blazer or sportcoat is not a suit. These things are similar to suit jackets, but they are only jackets, and don't come with matching pants.
Pants are not a suit. You knew that.
A blazer and pants still are not a suit, because they don't match. If they do match, it's not a blazer, it's a suit jacket. If they almost match, then they don't match. If you go buy some charcoal pants from J. Crew and then you get a similar-looking charcoal blazer from Bonobos, you do not have a charcoal suit. You should never wear those two together, or you're going to look like you're trying to wear a suit, and failing. If you pair your charcoal pants with a navy blazer, you'll look fine (if not great), but you still will not be wearing a suit.
A bathing suit is not a suit. Or, well... it is, given a very different definition of "suit," which is something like "outfit," which makes sense, because a bathing suit is a one-item outfit. Jumpsuit has a similar root. That's not the definition we're using, because if it was, this article could never end.
A birthday suit is not a suit. Do not go to your cousin's wedding in your birthday suit. Yes, I know you got it for cheap, but your uncle will punch you in the face.
What's kind of a suit?
Sweatsuits / Track Suits / those shitty "Juicy" combos girls wore in high school are not not suits. They meet the definition, I guess. You think of one thing when you hear the word "suit," and that's what this guide is about, but if I tried to write a definition of "suit" that excluded these things, I'd probably end up excluding something an avant-garde fashion designer invents eight years from now that I don't want to exclude. I like vague definitions, since they make language flexible. So... Fine, these are technically suits, but I am not talking about them.
On the other hand, I'm totally talking about tuxedos or dinner suits. I'm going to try to get into morning dress or white tie with tails and stuff too, although I've never been invited to a monarch's birthday party... But, let me put it this way: cashmere is a type of wool, but if you have cashmere, you don't use the word wool. A tuxedo is a type of suit, but you won't call it that most of the time. And the reason is... Tuxedos and "lounge suits" (or "regular" suits, or, if you they're dark colors, "business suits") are used for completely different reasons. A lot of people don't realize this, so let me dig in.
Tuxedos are for parties. "Lounge suits" are, confusingly, for serious business. A lounge suit is supposed to be a little boring. It's supposed to make you look put together, the way you want your accountant to look for the five minutes you meet with him -- and then you go home, and think, "that guy really has my money safe." Don't wear a tux to a business meeting. And as common as it is, it's a little funny to wear a lounge suit to a wedding -- particularly if the invite says "black tie," which basically means "your suit should be a tuxedo." "Black tie optional" is what most people see when they read the words "black tie." And I mean, that makes sense, because a lot of people can't afford to own both tuxes and lounge suits, and a lot of people need lounge suits. But the effect of all this is, when you see a tux, you think, damn, now that guy came to party.
Meanwhile, full evening dress -- that is, white tie -- and morning dress are not just party clothing, but attire that is really proper to a very particular type of event. If you wear white tie to a black tie event, you're going to look silly -- you're going to look like a stuffy old British butler. But if you get invited to a white tie event, or an event whose invitation demands morning dress, you'd best follow the rules. There are also stroller suits, which are kind of morning suits, but less formal, but still more formal than a lounge suit. White tie is generally reserved for royal events, balls, and other fancy events. Some musicians below report that they've had to wear white tie for their roles in certain events. Morning dress is also often used for royal events, but may also be used for daytime weddings and the like. Both are more common in Europe than the US.
A typical suit is composed of two matching pieces -- a jacket and pants. Sometimes, it'll include a matching vest.
A suit jacket is typically a long-sleeved jacket with a buttoned front. The buttons start way down, and you don't really have a neckline -- you have a deep v-shape leading to the first button somewhere around your navel (see button stance for details about where that ends). Now, you know how there's a folded-over padded sort of thing along the v-shape? Those are the lapels. Look at this shit. Those things. I'm going to use the word "lapels" a lot, so make sure you understand what I just half-explained. In white tie, your jacket will be a tailcoat. In Morning Dress, your jacket will be a morning coat. Those are cut differently, with the tailcoat having... "tails."
A single breasted jacket (I'll explain what that means later) might have one, two, or three buttons... don't have more than three. Sometimes, you'll see a "three roll two," which means "three buttons, but the top one is on the bottom of the lapel, right around where it rolls." This is actually not nearly as weird as it sounds. The button isn't supposed to be buttoned, but it's a detail that, for some arbitrary reason, suit nerds like. While we're talking about it, suit nerds love talking about the lapel roll.
The lapel should have what looks like a buttonhole in it meant for boutonnieres (those flowery things). Cheap suits might skip that hole, or include it but not even bother making it functional. Nice, handmade suits might have a Milanese button hole, which involves a few hours of hand-sweing... Yes, for just the buttonhole. Sounds wasteful, huh?
The jacket also often has a few pockets, and they're mostly for show. You'll almost certainly have a left breast pocket on the exterior for show or for pocket squares. You're also likely to have an interior pocket or two -- I usually see one on the left side. These are useful for a small item like a slim wallet or passport or kippah (or yarmulke, for you Yiddish folks). As for side pockets: "Flap pockets" are the most common thing you'll see -- they're the flaps on the sides of suits, and the pockets under them. They're formal and standard. "Patch Pockets" are just kind of sewn on top, and look casual. "Jetted Pockets" are sleek little slits in the side -- those are generally good for tuxes. A "ticket pocket" is a funny little detail like the 3-roll-2 thing above -- it's an extra pocket above your right pocket, which, once upon a time, was used just for train tickets. Yeah, I don't get it either.
There might be "vents" in the back of the jacket that might help you move more freely without shoving the jacket around. Zero, one, or two vents are all reasonable. I'll let you pick what you like. Center vents are historically related to horseback riding, so they're not appropriate for eveningwear.
Your suit has a shoulder that might or might not be padded. I'll talk about that with construction.
And your suit's sleeves have cuffs. Hopefully these cuffs have buttons on them. Those buttons might just be for show, or they might be functional ("surgeon's cuff"). If you're going to get a cheap suit, it's actually better if they aren't functional, because that makes your sleeve length easier (cheaper) to tailor. If you get an expensive suit, functional cuffs are a good idea. Some people like a contrasting buttonhole on one of the buttons... But I don't. Eh. It's a flashy detail. The buttons might be super close or not even touch."Kissing" buttons barely touch. Those are good, because they vaguely imply handwork. "Stacked" buttons are practically on top of one another.
Pants or trousers or slacks or suit pants are... You know, they're the things you put on your legs. If you're not Thom Browne, they're going to be long pants. They are made of matching materials, in matching colors, in matching weaves, to the suit jackets they are paired with.
How do you get these pants to stay up? Either a belt, side adjusters, or suspenders.
Most of the trousers you've seen have belt loops for a belt. But belts add a little bulk, and they cost money, and a lot of people think: "eh. I don't need that shit." And you don't! You don't really need anything, but at the very least, it's good to have side adjusters, which might be buttons or metal slidey things on the sides of the waist that help you tighten them up after they're already on. Or, you can have little buttons inside that connect to suspenders or braces -- those are great, but shouldn't be seen -- wear a jacket or sweater or something on top of them.
Trousers also have a fly, usually with a zipper and either a button or a slidey thing (or both). Hopefully, some part of the closure is off-center, which helps everything stay in put because... idk, torque something something. There's a word for this. What's the word?
The ankle part of your trousers will either be cuffed or not. "Cuffed" here means that the bottom is folded up, but not the way you roll up your jeans -- no, it's folded up by the tailor, and since your pants are tailored to your length, it looks intentional. This comes down to personal preference.
I'd prefer you didn't wear one, but if you must... A vest or waistcoat has a front facing made of your suit's body/shell material, and a back facing that is probably made of the same thing as the lining, I think, I don't really know. Nobody's ever going to see that rear facing, but if it's wool, you'll melt. Waistcoats are required in, and have special rules in, White Tie and Morning Dress.
So, again, a suit has a body (or shell) material, some kind of canvas or something, and (usually) lining. A tuxedo will have a separate material for its lapel facings and stripe. We're going to talk about the canvas in construction, but essentially, it's supposed to be made of horsehair.
The bodies or shells of most decent suits are made of worsted wool. Wool might include mohair or cashmere or vicuna, but if it does, you'll know it. What the fuck does worsted mean? Well, a lot of things -- it's twisted and treated and some such... but the most tangible definition is... It's the suit stuff. You know. The kind of wool they make suits out of. Yeah. That stuff. Specifically, the worsting process involves treating and twisting the wool so that it's kind of... less fluffy, if that makes sense. You might describe it as "hard," which... you know it's not hard, but it's harder than woolen. Woolen refers to the softer type of wool yarn.
Why wool? Wool is expensive. Why don't we use something cheaper, like cotton or polyester? Wool is fucking great. I love wool. Guys, guys, guys. Wooooool. It's warm, but breathable. It's wrinkle-resistant. It handles water well, but repels odors by magically destroying germs, even though nobody asked it to. It's durable enough to justify its cost at all tiers. And it's easy to care for. You almost never need to take wool to the dry cleaner, unless it gets stained or really stinks. You might clean denim more often than you do wool. Hey, u/materialsnerd, I'm linking to your thread again.
You will often see a "super number" in a suit's description, such as 120s or 150s. "Super" is an old marketing term that described really good wool. All you need to know now is: 100s is thick (good for winter), 150s is fine (thin, good for summer). Anything finer than 150s is generally not recommended, since it will wear very quickly and feel flimsy. Such fine fabrics are generally very expensive. Everything from 100s-150s is within standard range, but ~120s is a good weight for a versatile, affordable, quality suit that will last a long time.
The standard suit weave is twill, but you're also going to want to know about flannel, tweed, herringbone, sharkskin, birdseye, fallie, and seersucker... some of which are variants on twill. Real Men Real Style has a very handy guide on this.
Tweed is an inherently ambiguous word that refers to some kind of really great, thick, warm, rough, soft wool. After a while, you'll just know it when you see it.
As with everything, there are some suits made of cheap polyester. Don't buy one of those if you can avoid it. You'll bake, and smell, and look bad, and it's really not too hard to find a cheap wool suit.
Cotton is also usually cheap. It doesn't handle moisture or odor well, so you'll need to get it cleaned very often. It wrinkles more than wool. It's not as breathable as wool (in case you wanna go unlined). Cotton kinda sucks in all the ways wool is amazing. Sometimes it's used in blends with linen. It can also take the form of chino or seersucker.
Sometimes, you'll hear people talking about a chino suit. Chino is a type of cotton fabric that you can feel if you have a pair of chinos. If you have a pair of khakis, those are chinos in an ugly color. If you have cargo pants, those are probably chinos with ugly pockets. You know what chino is now, right? , but it's not so formal -- a little wrinkly, and stuff.
You've also heard of seersucker, maybe -- yeah, sounds funny, right? Seersucker is a kind of crunchy cotton. Seersucker is pretty breathable and pretty wrinkly.
Linen is amazing, but not ideal for suits. Linen wrinkles like crazy. If you look up photos of linen suits, you will see nothing but lies. That's what a linen suit looks like the moment you put it on, and then you move and it is wrinkled beyond the domain of the world's most powerful iron. That said, you might see some linen blends with cotton or silk where this downside is mitigated. Oh man, I tried a linen/silk blend unstructured double breasted blazer from Ring Jacket a couple of weeks ago, and... stay focused, /u/danhakimi, you're on a mission. The main upside of linen is that it will breathe amazingly, and you'll stay cool wearing it in the summer, and you'll fall asleep and wake up and think ugh, everything should be linen. it's also pretty good with odor, and generally just magical, except for the wrinkling.
Wool blends might be a few different things. They might be a blend of wool with bad things like polyester -- avoid these if you can. They might be a blend of wool with good things, like linen or silk -- those are tricky, and unique. They might wrinkle, or they might not. Other blends exist too -- I've been seeing some linen/silk blends recently, and desperately want something like that unstructured. You'll see cotton/linen and a few other things too. And you might just see a blend of different kinds of wool, like a wool-cashmere blend. Cashmere doesn't generally last as long as other kinds of wool, but it's soft and warm and expensive, so... Go for it, if you can.
Finally,the body of a tux might be made of velvet. Wool is more common, it's still definitely the norm, but Velvet is a thing. Except for certain details -- we're getting to that.
... Okay, so that's body materials. Fuck, I write a lot.
Lining is actually optional. But usually, it's polyester, rayon, cupro (a cotton by product that's better than cotton because cotton sucks), acetate, or silk. Bemberg is a synthetic silk that is kinda like rayon, but great.
Unlined suits (which are sometimes but not necessarily unstructured) are awesome. They breathe nicely and feel soft. They'll be finished on the inside with the same material as the body. You can also go half lined, but I'd personally go all or nothing.
But the lining is sometimes nice too. It adds a little weight, structure, and insulation. It puts an extra layer between you and your suit and your body, which might help if you sweat a lot. Finally, it's a chance to give your suits a unique touch, especially if you want to customize them -- your lining is usually invisible, but the tiny flashes make for a very slight accent, even if you go with a funky color or loud pattern. It might even be cheaper to use lining, since you don't need to worry about finishing the interior in wool.
Polyester doesn't breathe. A lot of suit makers cheap out, and even if the body is wool, they'll use polyester linings. That sucks. Polyester sucks. You'll bake in it. Or even in the winter, it isn't comfortable. It will probably last forever, though.
All those other lining materials I mentioned are fine. You don't really care any more, do you? I mean, there's guides out there.
Oh, one more note -- your buttons on a lounge suit might be plastic or horn. Better suits use horn.
Alright, so what's the deal with tuxes? Dinner jackets have lapels face in either grosgrain (silk) or satin (silk). The matching trousers will have a stripe going down the side made of the same material as the lapel facing. The buttons will all be faced with the same material. All of these will be the same shade of black. And you will wear a bow tie made of the same material. Remember the words "they have to match?" Yes. That, again.
A morning jacket is similar in material composition to a dinner jacket, except the wool has to use a barathea or herringbone weave. The waistcoat should be a marcella or piqué cotton, with a matching shirt and bow tie... which each have even more rules.
Alright, so the first thing suit nerds want to talk about every morning is canvas. Canvas is a magical thing in between the outer layer and inner layer of your suit. This helps give the suit its shape. A suit is supposed to provide your body with some structure -- that's especially important on flabby men like me, but still looks good on, you know, Daniel Craig. Quality horsehair canvas will mold to your body over time and fit better and look better and make you happier.
Cheap suits might use a "fused" or "fusible" canvas, which might be synthetic and connected to the suit with glue. This causes the jacket to move in a silly way -- the parts that are supposed to move together don't, or the parts that are supposed to move independently don't, or both. And when you get them dry cleaned, the glue might cause shitty bubbles. So a fused suit is cheap and not very good. (If you're between a fused wool suit and a half canvassed polyester suit, I vote wool. Wool is great. Polyester sucks.) Macy's and JCF make these as well as anybody in the $150 range.
Then, you have middle ground #1, which is a "floating chest piece." These use a little bit of horse hair, but only in the chest. It doesn't reach the lapels, or the bottom of the jacket. These are somewhat uncommon. Some people will sell them, but advertise them as half canvassed, because they're jerks. Off the top of my head, Banana Republic sells a floating chest piece, for roughly $300 on sale.
Then, you have half canvassed suits. These are canvassed in the chest and lapels, which causes the lapels to roll in a cool way. That's good. SuitSupply sells these in the $400-$500 range. The parts that aren't canvased don't really need much shape anyway, but they might wear a little faster than the chest, and that's not ideal. The parts that aren't canvased, in this case, are generally fused, which sucks.
The top tier here would be full canvas (aka canvassed by elitists who view everything as either fused or canvased). That is the whole body (not including the arms or pants). This will last longer, and look marginally better, but cost more. Up to you if you want to splurge. These usually cost more than $500.
Finally, off to the side, you have unstructured suits with no canvas or padding (or very little). They are often also unlined, which means the jacket is really just shell. These are, as you might have guessed, less structured and more flowy. They're lighter and more breathable (obviously, since you got rid of layers). They're on the casual side, but not necessarily too casual. They feel great. Ugh.
Shoulders often have some amount of padding. Unstructured suits often have none. Italian-style suits have little. British-style suits have a lot. A formal suit should at least have some. This relates to preference, but also to other details, and whether you want a cohesive suit.
Pick stitching is very subtle but visible stitching you can see around the outer edge of your lapels. It signifies that the lapels were hand-padded. You want this. You might think it looks funny, but you definitely want it.
I forget the word for it, but nice handmade trousers will have a little corner thing at the sides which... I think helps keep the pants flexible? Somebody remind me what this is called and what it's for.
You might have noticed a pattern by now. A lot of details are thought to be "better" because they have to be made by hand. Spending four hours on one button hole is silly. So when you see a button hole that was stitched by hand for four hours, you know that somebody has waaaay too much money. You want to look like you have way too much money... and you know how to use it on things that fancy people like. That is a good thing.
A suit can come in one of three lapel styles, single or double breasted, and as a lounge suit, dinner suit (evening dress), dress suit (full evening dress), or morning suit, or a stroller suit.
Lapels can be notch lapels, peak lapels, or shawl lapels.
Notch lapels have a sort of square notch cut out near your neck. This is standard for a business suit.
Peak lapels are a little more interesting. The bottom side sticks up and out, sharply. They look very different at different lapel widths.
Shawl lapels are funny -- they just curve straight up and down and around. These are strictly for tuxedos -- don't get a business suit with one of these. You should consider how much belly your shawl lapel has. Ideally, you want a little belly -- a slight curve -- as opposed to none -- a straight line. A large belly strikes me as an old style, but I'm not sure how true that is.
There are a few other kinds, like Tautz lapels, which nobody will expect you to know about. Those are kind of like peaks, except they point to the side.
You can also talk about the gorge of the notch or opening in your lapels. Higher gorges are more modern, lower and larger gorges have a classic feature to it.
Lapel width is very important -- I'll talk about that further down.
A jacket can be single breasted or double breasted. If you hear "1.5 breasted," that's a particular type of double breasted jacket.
Confusingly, single breasted jackets have two breasts. The majority of jackets you see out there are single breasted. The defining characteristic is that there is one vertical row of buttons (or one button) that shows up at the edge of the right breast for men, or the left breast for women (particularly wealthy women from back in the day when your servants buttoned your jacket while facing you). This creates a very small overlap between the breasts.
Double breasted, by contrast, refers to two vertical rows of buttons, and a large overlap. Recently, some companies have been using "1.5 breasted" as a corny marketing term for a double breasted jacket where the overlap is not that large, and the vertical rows of buttons are closer. Apparently, the advantage of this is that it looks better unbuttoned... but you don't buy a double breasted suit to wear unbuttoned.
Most suits you've ever seen are lounge suits or, if they're in dark colors, business suits. Single breasted lounge suits should generally come with notch lapels, but peak lapels aren't wrong, just a little silly. Double breasted lounge suits usually have peak lapels, which, with pinstripes, will place you in full 1940s gangster territory. Generally, for a single breasted lounge suit, you want two buttons, or a three roll two. Maybe three if you're tall and old-fashioned.
Dinner suits or tuxedos (eveningwear) are... Well, I've been talking about them for forever by now, so you know. They're the party suits. Don't wear them before 6pm or else they'll transform into gremlins. They shouldn't have notch lapels, less because it's wrong, and more because lounge suits have notch lapels, and you don't want to look like a boring accountant, you want to look like you came to party. Peak or shawl. Again, they can be single or double breasted, but a double breasted tuxedo is a real oddity. Generally, you want a one button tuxedo. You want to wear a tuxedo shirt with this, which is different from a regular dress shirt. Their trousers have a single stripe along the side in the same material as the lapel facing.
Note that "black tie" generally refers to a non-velvet tux in one of two specific colors: black, or midnight blue. Did I say navy? I did not. Midnight blue is darker than navy, and often shows up as darker than black in photos. The tie that the style is named after is not a necktie. You can wear a bow tie, or... well, a cravat might work, but that's a whole other discussion. Again, peak or shawl, with black lapel facings in grosgrain or satin. Creative black tie can involve crazy colors and velvet and double breasts and crazy prints and shit like that. Still no neckties.
Also note that a tuxedo can and must be worn with exactly one of the following: suspenders or braces, a matching waistcoat (in which case, you shouldn't button the button), or a cummerbund (the thick silky thing that goes around your waist but isn't a belt). Do not wear a belt with a tuxedo. Don't wear two of the above. Don't wear three of the above. Don't wear zero of the above. Don't buy a tuxedo with belt loops, it shouldn't have belt loops. If you're wearing it with a waistcoat or cummerbund, you probably want side adjusters on your trousers.
White tie describes a very particular type of suit (full evening dress), a weird thing with tails and way too many rules... paired with a low-cut white marcella waistcoat, and a very particular type of white shirt, and a white tie, all in a particular weave as described above. The suit should be black with peak lapels, and the lapels should again be faced in satin or grosgrain. The jacket is short in the front and cut in a particular way, whereas the tails in the back are very long. The jacket should not be buttoned, and generally cannot be buttoned. The pants might have a single or double stripe along the sides.
White tie should be paired with a shirt and bow tie that match the waistcoat. The shirt should have a single french cuff, and should be fastened with studs. The shoes should be patent leather opera pumps. You can optionally throw in a top hat, a cane, or white gloves. There are a thousand more rules, but this info should be enough to get you started talking about white tie.
A morning suit (for morning dress) is kind of like full evening dress, but crazier, and during the day. It's the one suit where your jacket and pants should contrast, in both color and pattern -- your pants should actually be pinstriped. The jacket is longer in the back, but unlike a white tie jacket, is cut smoothly, so that some of the length is evident from the front, and so that the back doesn't form "tails." The full length in the back should be about knee-length. The lapels are still peak, and is usually some kind of gray or black. The waistcoat should be made of the same material, but in a different color.
A stroller suit is the informal equivalent of a morning suit, although still more formal than a lounge suit. I have no idea what makes it different from a morning suit, and honestly, if you care, you have too much time on your hands.
Measurements worth thinking about
Suits come in off the rack (or off the peg, or ready to wear -- otr or rtw), made to measure (or mtm), and bespoke. Off the rack suits come in fixed sizes. Made to measure involves a lot of measurements that are then sent abroad for cheap labor on a pretty good suit with some amount of personal customization. Bespoke involves multiple rounds of measurement and fitting over months with an amazing local tailor who will make you an insanely good suit that fits perfectly and can be customized however you want.
The primary size for any suit jacket is defined by chest and length. But the primary length "measurement" is just a choice between regular, long, and short. This length covers both the body and sleeve. Sleeves are pretty easy to tailor, so don't even trip about those, plan on getting them tailored. Functioning buttonholes are actually a little bit harder to tailor, but still not that hard.
Body length is a little trickier, since it also relates to button stance. Button stance is where the top button on the jacket sits on your body. I typically wear a 40s. If I got a 40L and shortened the sleeves and shortened the body, I'd still have an issue, in that the buttons would be waaaay down there. This can theoretically be tailored, but don't plan on it -- your tailor would have to sew over and redo buttonholes, shift the lapels, maybe move pockets, and do a bunch of other stuff you don't want done, even if your tailor is willing to try. Just get a jacket with a good button stance, and good body length.
Button Stance itself is important. It generally refers to the position of the top button that you're supposed to use, or the "buttoning point." For example, it would refer to the second button on a 3-roll-2 jacket. It should usually be around your natural waist, but shifting it up or down might be good if you want to shift proportions: a higher stance shortens your torso and lengthens your legs, and a lower stance lengthens your torso and shortens your legs. Some people also use the term "button stance" to refer to the distance between buttons, which is more interesting in double breasted jackets than single breasted ones.
The shoulder fit is also very important. You won't see it reflected in sizing, and it's usually kept in some proportion to your chest, so if your chest and shoulders are not standard proportions, you might have a slight issue with off-the-rack suits. This is very hard to tailor, so get it right the first time.
Lapel width is a different issue -- not really so much about fit, but proportion, and style. They're measured at the widest point. Skinny lapels are out -- they were a brief modern style. A classic suit as a decent sized lapel. Your tie width (at the widest point) should, in theory, match your lapel width. Note that this really transforms some of the above lapel styles. Slim peak versus super wide peak lapels are very different. Some shawl lapels go deep, and others are sleeker and cleaner (I like the latter, but the former is more classic).
Finally, it's worth mentioning arm holes. Not eye holes, no, arm holes. The hole at your shoulder that goes to your arm. You don't want them to be baggy. Off the rack, and even made to measure, these are going to have a little give, and go a little lower than your actual armpit. Off the rack, they have to fit everybody. MTM, they're still following a pattern and this is just a detail they won't handle. Bespoke tailors, on the other hand, can give you high, narrow arm holes, which will move beautifully with your body and help keep your posture and just make everything better. Ugh, I want a bespoke suit.
The arm hole's seam is called the sleeve head. Sven explains sleeve heads better in that video than I can in text. Again, these are something you'll worry about more when you get into customizing a suit, or buying unstructured suits, but some off-the-rack bands do interesting things with shoulder padding and structure, so even if you're just going to SuitSupply, it's worth understanding.
Now, for pants, we're worrying about waist, inseam, break, and rise.
If you're buying off the rack, waist is the first number. I generally wear a 32/30, which means a 32 waist. You know what pant waists are. (Your suit also exists at your waist, so this measurement is relevant to a good suit fit, but since they're sized by the chest, that relates more to your fit, off the rack).
The second number is inseam, which is kind of code for length. But it's the length of the seam on the inside -- IE, from your crotch down to your ankles. Where on your angles? That depends.
Do you want your pants cropped, or too short to meet your shoes when standing? That's pretty casual, I wouldn't recommend it. If you do it, you want your pants pretty slim. You can have no break, which means they just barely touch your shoes, or don't, but end right there, you know? That's a modern/young look -- perhaps too much so. A slight break, where the pants hit your shoes a little, is still pretty modern and young without looking bad to the partners at your firm. A medium break hits your shoes a little more, and starts to fold a bit, and is good, classic, and perfect for the partner, unless he's an old man, in which case he might try a full break, which really folds at the ankles and over the shoes. Pants with a full break should not be slim.
Note that inseam and break are probably the easiest things in the world to tailor. So again, don't sweat it when buying. A lot of brands sell pant legs unfinished, so you can handle this (and also decide whether you want to cuff the leg or not).
So, if the inseam is the length under the crotch, what's the length from waist to crotch? For some reason, that's called the rise. A lower-medium rise is pretty standard these days, and sits in the same place as most of your pants sit, above your hips. A high rise sits at your "natural waist," above your belly button, and is pretty classic, believe it or not. If you want to be talked into a high rise, go read https://streetxsprezza.wordpress.com/.
Off the rack suits sometimes have separate sizes for jackets and pants, but sometimes just tell you the jacket size and assume what your pants size would be. They call the difference between these sizes your "drop." If you have an unusually large or small drop, that really sucks. Either go for the brands that will sell you separate sizes, or go made to measure.
Finally, we can talk about fit. You don't want your suit too skinny. You're not buying it to go to hipster bars in Brooklyn. So you can go slim and modern, or regular and classic. Or relaxed. If you're buying off the rack, you want to use this to try to match your body and get something that actually fits well. If you're going MTM or bespoke, you know your suit is going to fit you, so you want to pick based on style -- not whether it fits, but how it fits. Do you want it to hang and flow a little more? Do you want to look tight and put together? I mean, you will look put together either way, but... You know, talk to your tailor, see where you want to land.
Alright, I know everything now, where do I buy one?
See our favorites at various price points, or Styleforum's hierarchical list by quality. Remember, fit is the most important thing! A high quality suit that doesn't fit properly is garbage next to a shitty suit that fits well. But you know enough now to get a good suit that fits well, right?
Special thanks to /u/ben_kh who helped me flesh out the white tie/morning dress portions. I got a good amount of info from Gentleman's Gazette on YouTube and the blog from Real Men Real Style -- and a bunch more than that, so if I forgot to credit you, I'm sorry!