Nobody is in charge of clothing sizes
Shoe sizes at least descend from a defined unit. Clothing sizes do not. There is no body enforcing what a US 8 or a UK 12 means, no legal definition, and no obligation on a brand to match anyone else. Each label draws its patterns over an in-house block -- a base body shape it considers its customer -- and sizes outward from there. Two brands can be equally consistent internally and two sizes apart from each other.
That is before vanity sizing, which is the slow relabelling of a given set of measurements with a smaller number. A US women's 8 in the 1960s was cut for a substantially smaller body than a US 8 today. The drift is well documented, it is not uniform between brands, and it is one-directional. It means a number from an old chart, an old garment, or your own memory of what size you take is not reliable evidence about a new purchase.
What to measure, and where
Four measurements cover almost everything. Take them over the underwear you would wear with the garment, with the tape snug but not pulled tight, and standing normally rather than holding your breath.
| Measurement | Where | What it sizes |
|---|---|---|
| Chest or bust | Around the fullest part, tape level under the arms | Shirts, jackets, dresses, knitwear |
| Waist | The natural waist, the narrowest point, roughly at the navel | Trousers, skirts, tailoring |
| Hip | Around the fullest part of the seat, usually 20 cm below the waist | Trousers, skirts, dresses |
| Inseam | Crotch seam to the hem on trousers that fit | Trouser length -- the second number in 32x34 |
Write them down in centimetres. Every brand size chart worth reading gives body measurements, and comparing your numbers against those is a far better process than converting a size you took somewhere else.
The conversions that hold, and the one that does not
Some relationships are stable enough to rely on. Men's tops are labelled by chest measurement in inches on both sides of the Atlantic, so US and UK menswear agree by construction. Women's UK numbers run four above US -- a US 8 is a UK 12 -- and that holds across most of the market. EU women's sizes run about 30 above US.
The one that breaks is Italian sizing. Italian womenswear numbers run roughly 36 above US, so an Italian 42 is around a US 6, not a US 12. Listings frequently label it simply "EU", and if you convert it as a French or German size you will be six sizes out. When a dress size in the low 40s appears without a bust measurement beside it, that is the ambiguity to resolve before ordering.
Where the number stops helping
Even a perfect conversion only handles one dimension. A shirt that fits your chest may be cut for a longer torso than you have, or with a slim taper that assumes a waist eight inches smaller than the chest. Trousers labelled with your waist may be cut with a rise -- the distance from crotch seam to waistband -- that sits somewhere you do not want it. Fit descriptions such as slim, regular, classic and relaxed are doing more work than the size number, and they are brand-specific too.
The reliable test for online buying is to measure a garment you already own and like, flat on a table, and compare those numbers with the flat measurements in the listing. Chest across the underarm seam, shoulder seam to shoulder seam, sleeve from shoulder seam, and total length. Retailers that publish flat measurements are giving you the only genuinely comparable data available, and the ones that publish nothing but S, M and L are asking you to guess.
Buying across borders
- Convert, then verify against the brand's centimetre chart. The conversion tells you which row to look at; the chart tells you whether it fits.
- Japanese and Korean sizing runs noticeably smaller than the equivalent US label. A Japanese L is often closer to a US M.
- Check whether an "EU" listing is actually Italian before ordering womenswear.
- Read reviews for consistent reports of running small or large. A pattern across dozens of reviewers beats any table.
- Factor the return cost into the decision. International returns often cost more than the garment, which changes the calculation from "order and see" to "measure first".
Questions people ask
What is a US 8 in UK sizes?
A UK 12 for womenswear. The UK numbering runs four above the US numbering across the standard range, and that relationship holds more consistently than most conversions here. For menswear the question does not arise, since both label tops by chest measurement in inches.
Why does an Italian 42 not convert like other EU sizes?
Italy uses a different numbering scale for womenswear, running roughly 36 above US rather than the 30 used in France and Germany. An Italian 42 is about a US 6 and a UK 10. Listings often say only EU, so the number alone is ambiguous -- check for a bust measurement in centimetres, which resolves it immediately.
The jeans I measured are two inches bigger than the size on the label.
That is normal on mainstream brands and it is vanity sizing. Measure the waistband flat, double it, and use that number when comparing against other jeans. Selvedge, workwear and Japanese labels tend to be much closer to their stated size, which is why switching between those and a high-street brand throws people.
Is alpha sizing, S M L, any use at all?
It is useful for knitwear, t-shirts and anything with give, where a size covers a wide range of bodies. It is close to useless for tailoring, shirts with a collar size, or anything fitted, because one letter spans two numeric sizes -- around four inches of chest. Where both are offered, take the numeric one.
How should I size children's clothes?
By height in centimetres, not by age. The EU convention prints the height the garment is cut for directly on the label, which is the least ambiguous system in use. Age labels are population averages, and children of the same age routinely differ by 15 cm, so the age on the tag is the least useful number on it.