It's one of the most frustrating things about buying shoes: you're a reliable size in one brand and a different number in the next, even though your feet haven't changed. You're not imagining it, and you're not doing anything wrong. Here's what's actually going on.
The Size Label Is Not a Standard
This is the heart of it. While UK, EU and US systems define what a size should mean, there's no tightly enforced standard that every manufacturer measures to in exactly the same way. Two brands can both print "UK 8" on shoes that are noticeably different lengths inside. The label is a claim, not a guarantee.
It Starts With the Last
Every shoe is built around a last, the foot-shaped mould that determines its internal length, width, and shape. Different brands use different lasts, shaped around their own idea of a typical foot. A brand whose last is cut long and narrow will fit completely differently from one built short and broad, even at the same labelled size.
Vanity Sizing
Just as with clothing, some footwear sizing drifts over time, and there's a commercial pull toward making shoes a little roomier than the label suggests so they feel generous. The effect is subtle in shoes compared to clothes, but it's one more reason the same number doesn't fit identically everywhere.
Different Shoe Types Fit Differently Too
It's not only across brands, it's across styles within a brand. A running shoe, a dress shoe and a boot from the same maker can fit differently because they're built on different lasts for different purposes. Athletic shoes often run differently from formal ones even with matching size labels.
How to Buy Around It
- Know your foot length in centimetres and treat that as your truth, not the label. Convert from it using the converter.
- Check the brand's own size guide where they publish one. Many list the internal length per size, which is far more useful than the number.
- Use your history per brand. Once you know you're a 9 in one maker and an 8 in another, record it. Your own track record beats any universal chart.
- When in doubt between two sizes, size up for closed shoes, and account for the socks you'll wear.
The Bottom Line
Your size varies between brands because the label isn't a strict standard, every brand builds on its own last, and shape matters as much as length. Anchor on your actual foot measurement, keep notes per brand, and the variation stops being a mystery and becomes something you can plan around.