You are not imagining it, and you have not changed shape between two shops on the same street. A size label is a brand's opinion, not a measurement.
Here is the part almost nobody is told: there is no enforced clothing size standard. The United States had a voluntary one, built from a 1940s survey of women's body measurements, and it was withdrawn in 1983. What replaced it — the ASTM tables — is voluntary too, and most brands do not follow it. Every label is free to decide what its own "M" means, and they all decided differently.
So a size is not a fact about your body. It is a fact about one company's fit model: the single real person, hired for a particular set of measurements, that the pattern was cut to and graded up and down from. Two brands with two different fit models produce two different size 10s from the same cloth.
The three reasons a size moves
The fit model. A brand aiming at 20-year-olds and one aiming at 50-year-olds hire different bodies and grade from them. Neither is wrong; they are simply not the same garment.
Grading. Going up a size is not a uniform scale-up. Each brand decides how much to add at the chest, the waist, the hip and the sleeve per step. Two brands can agree exactly on a size 8 and disagree completely on a size 18.
Vanity sizing. Labels drift downward over time — the measurements behind a given number get bigger while the number stays put, because a smaller number sells. The size on the tag has been slowly detaching from the tape measure for decades.
Add international systems on top of that and it compounds. A women's US M is a European 38, a UK 10 and a Japanese 9 — before any brand has applied its own opinion to any of them.
What the numbers actually mean
The conversion below is the reference ladder — the systems as they are defined, which is what a size chart can honestly tell you. It is the starting point at any brand, not the finishing point.
Women's — Shirt / T-shirt
USUnited States
EUEurope
UKUnited Kingdom
JPJapan
KRKorea
CNChina
XS
34
6
5
44
155/80
S
36
8
7
55
160/84
M
38
10
9
66
165/88
L
40
12
11
77
170/92
XL
42
14
13
88
175/96
XXL
44
16
15
99
180/100
XXXL
46
18
17
110
185/104
1X
48
20
19
121
190/108
2X
50
22
21
132
195/112
3X
52
24
23
143
200/116
Notice the column that is doing real work: the Chinese system prints height and chest in centimetres (165/88 means exactly that), and Korea's numbers are chest measurements too. Those cannot drift. A letter can.
What to do instead of guessing
Know your body measurements, once. Chest, waist, hip, inseam. They do not depend on anybody's marketing, and every brand's own size guide is keyed to them.
Read the brand's chart, not the letter. If the garment page gives centimetres, use those and ignore the S/M/L entirely.
Record what actually fit. The single most useful piece of information is not your "size" — it is that this brand, in this category, fit you at that size. Written down, that fact never expires and never needs re-deriving in a fitting room.
Keep the label. A care label carries the size in the system the manufacturer used, which is often not the one printed on the shop tag.
Common questions
Is vanity sizing real?
Yes. The body measurements behind a given size label have grown over the decades while the number on the label stayed the same, so an old size 8 and a current size 8 are not the same garment. Nothing prevents it — the US standard that once defined those numbers was withdrawn in 1983 and its replacement is voluntary.
Which size should I order when a brand is new to me?
Take the brand's own centimetre chart and compare it against your measurements — not against the size you usually wear. If the brand publishes no measurements, order the size that matches your usual one in a garment of the same cut and be ready to exchange.
Why does one brand fit me differently in two categories?
Because they are usually different patterns, often from different suppliers, graded separately. It is entirely normal to be one size in a brand's shirts and another in its jackets.
Do men's sizes have the same problem?
Less of it, because much of menswear is labelled by measurement — a collar or a waist in inches is a number that cannot drift. The letter sizes drift exactly as much as women's do.
The charts behind this
More guides
MeSize
Stop looking this up. Save your sizes once — yours, your kids’, whoever you buy for — and carry every system in your pocket.
