You wear a medium. You have always worn a medium. Then a medium from a new brand arrives and it fits like a small, or a tent. Nothing is wrong with you or with the order. Clothing sizes are simply not standardised, and the letter on the label means something different at every brand.
There is no universal size
There is no law or industry rule that says what a medium has to measure. Each brand decides its own sizes based on who it expects its customers to be, what its patterns have always been, and the look it wants. A brand aimed at athletes, a brand known for tailoring and a streetwear label will all cut their mediums for different bodies.
The table below shows it plainly. It takes the chest measurement for size M straight from each brand's own published size chart.
Where the differences come from
Who the brand designs for. Brands build their size range around a "fit model", a real person whose body is the template for the base size. Every other size is scaled up or down from them. Two brands with different fit models end up with different mediums.
Fit and style. A slim fit shirt and a relaxed fit shirt in the same size can be made for the same body but cut with very different amounts of room. Oversized streetwear is deliberately cut several centimetres bigger than a classic fit.
Region. Brands from different countries tend to size differently. European, UK, US and Asian brands often run on different scales, and the same brand can size differently in different markets.
Vanity sizing. Over the years many brands have quietly made their sizes bigger, so that shoppers fit into a smaller label. It is one reason a size from ten years ago can fit differently from the same size today.
Body or garment measurements. Some brands publish the measurements of the body each size is made for, others publish the size of the garment itself. Comparing one kind with the other makes brands look further apart than they really are. Our guide to reading size charts explains how to tell them apart.
What to do about it
- Stop trusting the label. Your size is a set of measurements, not a letter.
- Measure yourself once. Chest, waist, hip and inseam cover most clothing.
- Check the chart for every new brand. Even brands you know can change their sizing between collections.
- Know the measurement that matters. Chest for tops, waist and inseam for trousers.
Let the comparison happen for you
clothly keeps your measurements and reads each brand's own chart when you screenshot a listing, so the size it suggests is based on that brand's numbers rather than on the letter you usually buy.