Why do popular fashion brands intentionally make their sizing charts wildly different from their closest competitors?

A Size Label Is Part of the Brand’s Fit

A clothing size is not a universal measurement. It is a label attached to a set of garment dimensions, and brands choose those dimensions around the bodies and fit preferences they want to serve. One company may cut a relaxed shirt roomy through the chest; another may design a close fit. Even when both garments carry the same size, they can feel very different.

That variation can be intentional. A distinctive fit gives shoppers a reason to return to a brand whose clothes reliably feel right to them. The label and the cut work together: once customers learn which size suits them in that brand, they have an easier path to buying again.

The Label Can Shape the Shopping Decision

Some brands also use vanity sizing: assigning a smaller size label to measurements that might once have received a larger one. A shopper who sees a more flattering number may feel better about the purchase, while a brand hopes to make its products more appealing. But the practice is not a shared system. A label that sounds reassuring in one store may correspond to a different fit in another.

The incentive is commercial, but the result is a costly tradeoff. Familiar labels can encourage loyalty, yet inconsistent sizing makes comparison harder and can lead to failed purchases and returns—especially online, where shoppers cannot try clothes on first.

Why the Differences Persist

Brands also build patterns around different intended customers, styles, and fabrics. A stretchy garment can fit a wider range of bodies than a rigid one; a tailored jacket needs different proportions from a loose sweatshirt. Those design choices are reflected in each company’s pattern and size chart, rather than in a single industry-wide standard.

So the number on the tag is a weak guide to whether a garment will fit. The more useful clues are the brand’s own measurements and how a particular cut is meant to sit on the body. That is why a shopper can wear different labeled sizes across stores—and still be buying clothes designed to fit as intended.