Why the Same Shoe Size Fits Differently Across Brands

Everyone has a version of this story: you're a reliable size 10 in one brand, but the same size in another brand feels a half size too small, or strangely roomy. The usual conclusion is that shoe sizing is basically random, every brand making up its own numbers. We went and checked the actual published size charts to find out, and the real answer is more interesting than that, and a little surprising.

The size charts mostly agree with each other

We pulled the official size charts from several major brands and compared the actual foot length listed at each US size. Nike, Brooks, and ASICS all list the same length at the same size: a size 8 is 26 centimeters, a size 9 is 27 centimeters, a size 10 is 28 centimeters, across all three. Not similar. The same number.

That's not really a coincidence. Most US athletic and casual footwear brands are built around the same shared length convention. If sizing were actually arbitrary, you'd expect these numbers to drift brand to brand. They don't.

So what's actually different?

If the length at a given size number is mostly standardized, then the thing making a shoe feel bigger, smaller, or narrower isn't the size chart at all. It's everything the size chart doesn't measure: toe box width, the volume of the shoe around your foot, how much the upper material stretches or holds its shape. Two shoes can share an identical nominal length and still feel completely different, because one wraps snugly around the foot and the other doesn't.

This is also why "runs small" and "true to size" aren't contradictions of the length chart, they're describing something the chart was never built to capture. A shoe can be exactly 27 centimeters inside and still feel tight if the toe box is narrow, or roomy if it isn't. The size number tells you the length. It doesn't tell you the fit.

A few real examples

• Hoka tends to run true to size by the numbers, but its wide toe box can feel roomy on a narrower foot, even at the "correct" size.
• ASICS Gel styles run true to size overall but noticeably narrower through the forefoot than the brand's other lines.
• Nike tends to run about half a size small in practice, which is a fit character on top of the shared length scale, not a different number on the chart.

None of this is something you can see by comparing two size numbers side by side. It's brand-specific knowledge, and it's exactly the kind of thing that's easy to lose track of when you're trying to remember how five different brands each fit.

We built a tool for exactly this

Since this keeps coming up, we put together a page that does the comparison for you: pick any two brands and see how they actually stack up, length and width both, in plain language instead of a chart you have to interpret yourself. It's built on the same brand fit notes ShoeCompass already uses in every recommendation, not a guess.