We bought a plain size medium t-shirt from twelve retailers, from a supermarket to a designer label, and measured every one flat across the chest. The narrowest was 48 centimetres. The widest was 55. That is a fourteen-centimetre spread on a garment sold to the same nominal customer under the same nominal size, and it is entirely normal.
How this happened
There is no enforced standard. Each retailer maintains its own size chart, built around its own fit model, and adjusts it over time in response to returns data and to a slow inflation known in the trade as vanity sizing. Because those adjustments are commercial rather than coordinated, the charts drift apart, and there is no mechanism pulling them back together.
Menswear and womenswear drift at different rates, too. Numeric womenswear sizing has inflated far more aggressively over thirty years than the chest-measurement conventions used in menswear, which is why a woman's size 12 from 1994 and one from today are not remotely the same garment.
The cost lands almost entirely on the customer and on the returns system. Online return rates in apparel run between twenty and forty per cent depending on category, and fit is consistently the largest single reason given. Every one of those returns involves two journeys, a repack, and often a garment that is never resold at full price.
“We know exactly what our medium measures. We just cannot tell you what anybody else's does.”
A technical manager at a UK retailer
The workaround that actually works
Ignore the letter and read the measurements. A growing number of retailers now publish flat garment measurements — chest, length, shoulder, sleeve — alongside the size chart, and those numbers are comparable across brands in a way that S, M and L simply are not. Measure a garment you already own and buy to that number.
The retailers doing this are seeing the benefit. Two told us that publishing flat measurements cut fit-related returns by double digits within a year, which more than covered the cost of measuring every style. It is the rarest thing in retail: a fix that is cheap, unglamorous, and demonstrably works.
Why nobody fixes it
A standard exists. Several do, in fact, and they are largely ignored, because the first retailer to adopt one alone would find its garments suddenly appearing to run smaller than everybody else's. Vanity sizing is a collective-action problem: any individual move towards accuracy reads to the customer as the brand having shrunk its clothes, and shows up immediately in returns and complaints.
That is why the practical fix has been to publish measurements alongside the letter rather than to change the letter. It sidesteps the trap entirely — the marketing size can stay wherever the market has drifted, while anybody who cares can buy on numbers that mean something. It is not elegant and it works, which describes most durable solutions in this industry.
There is one place the letters still work, which is within a single brand over time. If a retailer's medium fitted you three years ago it will probably still fit you now, because the drift is slow and internal consistency is the one thing every size chart genuinely delivers. That is why people become loyal to brands that fit them and why they are so reluctant to try new ones online.
Until flat measurements are standard, the letter on the label is best understood as a rough marketing category rather than a specification. Treat it accordingly and your return rate, and everybody else's carbon footprint, will improve.
