Underwear After Weight Loss or Weight Gain
Your body changed and the drawer did not. Underwear size after weight loss or gain: why hips beat waist, and why a stretched waistband never recovers.
Vanity Sizing: Why You Are a Different Size in Every Shop
No brand has to agree with any other on what a medium is. Why your size changes shop to shop, and how to buy by the measurement instead of the letter.
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There is a drawer in most houses that tells the story better than any article can. In it are three pairs of underwear, bought in the last two years by the same man with the same waist. One is labelled M. One is labelled L. One is labelled XL. All three fit.
Most men take this personally. They assume they have got fatter, or thinner, or that some shops are simply lying. The last is closest, but not quite right either, because lying implies a truth to depart from, and in men's underwear there very nearly is not one.
What you are running into is not your body being inconsistent. It is a system with no referee.
Nobody is in charge of the letter M
There is no law, anywhere, that says what a medium men's brief has to measure. Not in Britain, not in Ireland, not in the European Union, not in the United States, not in Japan. A brand can print M on a garment cut for a 76 centimetre waist and a brand next door can print M on a garment cut for an 89 centimetre waist, and neither has broken a rule, because there is no rule of that kind to break.
What does exist is a scattering of voluntary schemes. Europe has a standard for how size labelling should be presented, built around body measurements rather than letters. The Americans have voluntary measurement tables published by their standards association. Japan and Korea both have national industrial standards covering garment sizes, which is a large part of why sizing in those markets feels more orderly than it does here.
Every one of those is voluntary. A brand can adopt one, adopt part of one, adopt one and then quietly grade away from it, or ignore the lot. Most ignore the lot, because sizing is not really a labelling decision. It is a pattern decision.
So "medium" is not a measurement. It is a name a company has given to the second-smallest thing it makes.
Every size chart is one man, stretched
This next part explains almost everything, and it is not widely understood outside the trade.
A brand does not begin by deciding that a medium is 84 centimetres. It begins by drawing one pattern, in one size, on one body. That body belongs to a fit model: a real person, hired for the job, whose measurements the brand has chosen as its reference. The garment is fitted on him, adjusted on him, argued over on him and signed off on him.
Then the pattern is graded, which means scaling it up and down in steps, adding a set amount to the waist here, a smaller amount to the leg opening there, a little to the rise, according to rules the cutter has decided on. Every other size in the range is a mathematical relative of that one man.
Two things follow, and both are why you are a different size in different shops.
The first is that the whole range inherits his proportions. If the fit model has a modest waist and generous thighs, every size will be relatively generous through the thigh. If he is long in the body, every size will be long in the rise. You can feel it immediately: some labels seem to have been drawn for you, and others seem to have been drawn for a man you have never met. They were.
The second is that grading is not the same everywhere. One brand steps its waist by four centimetres per size, another by five, another by six. Two ranges can agree exactly at medium and be a full size apart by double extra large, which is why the problem worsens sharply the further you sit from the middle The Best Underwear for Big and Tall Men.
None of this is malice. It is what happens when a thousand companies solve the same problem independently, from their own starting body, and nobody compares notes.
The geography is real, and it is not imaginary snobbery
Layered on top of every brand's own drift is a genuine regional pattern, and it holds well enough to be useful.
Japanese and Korean sizing, broadly, runs smallest for a given letter. A Japanese L is not an insult and not a mistake; it is a size drawn for the population it serves, and the national standards behind it are more closely observed than anything equivalent in the West. Men used to British or American labels routinely find themselves two letters up buying from a Japanese brand, and nobody in that transaction has done anything wrong.
American sizing, broadly, runs largest. An American medium in a mainstream mass-market brand covers ground a continental brand would call large.
European and British sizing sit between the two and, crucially, do not agree with each other either. British high street sizing has drifted in the American direction over the decades without going the whole way. Continental sizing, particularly the German and Swiss houses, runs closer to the body measurement it claims, partly because those brands so often label numerically and a number is harder to fudge than a letter Slip: Why European Briefs Fit Differently. Italian sizing runs tighter than German sizing at the same nominal number. French sizing goes its own way and always has.
So: four or five overlapping conventions, no conversion table that survives contact with reality, and a letter that tells you which shop you are in rather than what size you are.
Vanity sizing proper, and mere chaos
These get lumped together and they are not the same animal. Only one of them is aimed at you.
Vanity sizing proper is a deliberate drift downward in the label relative to the measurement. The garment gets bigger and the letter stays the same. It is done because a man who takes a medium feels better about himself than a man who takes a large. It is best documented in womenswear, where the drift over recent decades has been dramatic, but it exists in menswear too, and is easiest to spot in trousers, where a waistband labelled 34 inches has a long history of measuring rather more than 34 inches.
The second thing is simple inconsistency, and it is far more common in underwear. Nobody at the brand decided to flatter you. Their fit model happens to be who he is, their grading rules are what they are, and the letter was never meant as a claim about the world.
Vanity sizing is directional: it always runs one way, so you can anticipate it. Inconsistency runs whichever way that brand's pattern table happens to run, so you cannot anticipate it at all. One is a marketing decision and the other is an engineering accident, and most of what you meet in an underwear drawer is the accident.
Why underwear is worse for this than trousers
Trousers have one saving grace. Most men's trousers carry a waist measurement in inches or centimetres printed on the label. That measurement may be optimistic, sometimes considerably so, but it is a number in a unit, and a number in a unit can be checked with a tape measure. You can catch a brand at it.
Underwear usually carries a letter.
A letter cannot be checked. It has no unit and no referent. There is no measurement it claims to be, so it cannot be wrong, so it cannot be caught. When a brand's medium drifts two centimetres bigger between one production run and the next, nothing on the packet changes and nothing could have, because the packet never said anything falsifiable in the first place.
The second-order problems make it worse. Underwear is stretch fabric, so the finished measurement depends on the knit and the elastane content as much as on the pattern, and two garments cut from one pattern in different fabrics will fit differently How to Read a Composition Label. It is nearly always sold sealed, often excluded from returns on hygiene grounds, and frequently sold in multipacks, so the ordinary correction of trying two and sending one back is not available Against the Multipack.
A category with no unit on the label, no returns and no browsing is one where sizing chaos persists indefinitely. Which it has.
The trap of the pair you are wearing right now
The most common mistake is also the most reasonable-sounding one: you look at the label of a pair you already own and like, and you buy that letter from the new brand.
It fails in both directions and it fails silently. The letter you are reading is a fact about your old brand's pattern table. Carried across, it is worth nothing, and the new brand's medium may be built around a body four centimetres away from the one your old brand used.
There is a slower version that catches men over years rather than in one order. You settled on a letter in your twenties and have bought it ever since, absorbing every drift along the way by adjusting your idea of what underwear is supposed to feel like. A waistband that rolls is normal. A leg that rides is normal. A seat that bags is normal. None of that is normal; it is a size error you stopped noticing. If your body has changed in that time, and most bodies do, the letter is connected to even less Underwear After Weight Loss or Weight Gain.
The tell is easy. If you have ever thought "this brand comes up small", you have caught yourself at it. The brand does not come up small. It comes up as itself, and you compared it to a letter from somewhere else.
What to actually do, with a tape and a chart
The fix is unglamorous and it takes about ten minutes, once.
Get one honest number. Put a soft tape around your hips where the waistband will actually sit, which for most briefs and trunks is on the hip bone and lower than a tailor measures for trousers. Stand normally, do not hold your breath, do not pull the tape tight. Write it down in centimetres, because almost every chart gives you centimetres and converting each time is how errors creep in. If your waist and hips are far apart, write both down; a lot of fit trouble is really a waist-to-hip ratio the brand did not plan for, which is the same reason some men have to think about the thigh separately Underwear for Big Thighs: The Chafing Problem Solved. A cheap soft cloth tape measure earns its keep here.
Buy the range, not the letter. Every serious brand publishes a chart mapping its letters to a measurement range. Find your number in it and buy whatever letter sits next to it, however unfamiliar. Ignore what you took from another brand, and ignore the letter's implications about you, which are nil. A brand that publishes no chart at all has told you something.
Handle the boundary deliberately. When your number falls at the join between two sizes, the fabric decides. Something with meaningful elastane, four or five percent and up, will accommodate you, so take the smaller size. A stable cotton rib or a wool knit will not, so take the larger. A cotton rib brief and a modal stretch trunk at the identical stated measurement are not the same garment on the body, and no chart will tell you that.
Keep a note. Everybody skips this and it is the step that actually ends the problem. A line in your phone: brand, size taken, whether it was right. Six entries and you never guess again. It reads as fussy for a month, then saves you every time a favourite gets discontinued.
Treat the first order from a new brand as a test. One pair, not six. Wear it for a full day, including several hours sitting down, which is where rise and gusset errors show up and where nothing on a hanger will warn you. Then buy the rest The Drawer Audit: How Many Briefs You Need and When to Replace Them. A merino brief bought five at a time in a sale, in the wrong size, is an expensive way to learn this.
Read the fit description too. Words like "close fitting", "athletic cut" or "relaxed" are the brand telling you, in the only language available to it, where its fit model sat relative to the average. It explains more misfits than the numbers do How a Brief Should Actually Fit.
The letter is not about you
What is worth taking from all of this is a small reassignment of blame.
The letter on the label is a fact about a company: who they hired to fit their patterns, how their cutter chose to grade, which market they drew for, what their factory does at a given tension. It is not a fact about your body, it has never made any claim about your body, and it is not a verdict on how the last few years have gone.
Men take sizing personally in a way they do not take, say, shoe width personally, mostly because clothing sizes have been made to feel like a score. They are not a score. They are an inventory code, printed on a pair of underpants, by somebody who has never met you.
Measure once. Write it down. Buy the range and not the letter. And when a new brand tells you that you are an extra large, take the extra large, wear it, and enjoy something that fits.
Once you know which sizes actually fit you in which shops, the next question is how many pairs you need in total, which is a separate sum and a simpler one. The drawer audit calculator works it out from your laundry cycle.
Questions people ask
Why am I a different underwear size in every shop?
Because no law anywhere sets what a men's underwear size has to measure. Every brand builds its patterns on its own fit model, grades outwards using its own rules, and prints letters that describe only its own range. Add genuine regional differences, with Japanese and Korean sizing running smaller and American sizing larger for the same letter, and the same body can honestly be a medium in one shop and an extra large in another. Buy by the brand's stated measurement range rather than the letter.
Is vanity sizing real in men's clothing?
Yes, though it is more pronounced in womenswear. Vanity sizing is a deliberate drift where the label understates the measurement, so a garment grows while its size name stays the same. It is easiest to spot in men's trousers, where a waistband labelled 34 inches often measures more. In underwear, most of what men experience is not deliberate flattery but simple inconsistency between brands, which runs in unpredictable directions rather than always in the flattering one.
How do I find my correct underwear size?
Measure your hips with a soft tape at the point the waistband will actually sit, which is on the hip bone and lower than a trouser measurement. Stand normally, do not pull the tape tight, and record the number in centimetres. Then read that number against the specific brand's published size chart and buy whichever letter it falls in. If you are between sizes, size down in stretchy fabrics with elastane and size up in stable cotton or wool knits.
Should I buy the same size as my current underwear?
No, not when you are switching brands. The letter on your current pair describes that brand's pattern table and carries no meaning at another company. Buy by measurement instead, and treat a first order from an unfamiliar brand as a test: one pair, worn for a full day including several hours sitting down, before you buy any more. Keep a short note of which size you take in each brand you use, and you will not have to work it out twice.