You're a solid 9 in one brand, a 9.5 in another, and somehow a 10 in a third. It's not you, and it's not that one of them is "wrong." Shoe sizing is a loose convention layered on top of wildly different foot molds, and once you understand why, you stop trusting the number on the box and start trusting your measurements.
There's no universal standard
US, UK, and EU sizing systems all measure differently and don't convert cleanly. A US men's 9 is roughly a UK 8.5 and an EU 42—roughly. Different countries even use different increments. So a brand that sizes in EU and one that sizes in US can label the same physical shoe with numbers that don't line up on any chart.
The last is the real culprit
Every shoe is built around a "last"—a foot-shaped mold. Two brands can use the same nominal size but completely different lasts: one narrow and low-volume, one wide and roomy, one with a long pointed toe, one round and short. The last shapes length, width, toe spring, and instep height. That's why a "9" fits like a glove in one line and pinches in another from the same brand.
Vanity and drift
Sizing also drifts over time and across markets, and there's a bit of the shoe equivalent of vanity sizing in fashion footwear. Athletic brands often run differently from dress brands too—running shoes frequently fit shorter because you want toe room for downhill strides, so many runners size up half.
How to cope without a fitting room
- Know your foot length in centimeters, measured properly. That number doesn't lie even when the size label does.
- Read the brand's size chart per product—the good ones state the foot length each size fits. Match the cm, not the number.
- Check whether a shoe "runs small/large/true to size" in reviews; it's crowd-sourced last data.
- Know your width. A brand that only makes one narrow width will never fit a wide foot regardless of length.
When you're between sizes
Sizing up half and taking up the extra volume with a thicker insole or an extra lace hole is usually more comfortable than forcing a half-size down. Feet tolerate a touch of length; they don't forgive being crushed in width. When in doubt on a snug last, go up.
The practical takeaway
Stop shopping by your "usual size." Measure once, know your centimeters and your width, and match them to each product's chart. Our listings publish the foot length per size for exactly this reason—so a Vailmoon size is a measurement you can check, not a guess you have to make.