Left and right feet are rarely perfect copies. When the difference is large enough, forcing both into one standard assumption creates a predictable compromise.

Most shoe sizing systems treat a pair of feet as one size because retail needs one label on the box.

Your body does not follow that rule.

Differences can appear in length, width or volume

One foot may be slightly longer. One can have more forefoot spread. An old injury can change volume. Dominance, activity and natural anatomy can all contribute.

Why the larger foot usually matters most

A shoe can be adjusted to improve security on a slightly smaller foot. It is much harder to create space that was never built into the shoe for the larger foot.

That is why, where a choice has to be made, the larger foot generally sets the minimum fit requirement.

But simply sizing up both shoes can create a new problem

Going up half a size may help the larger foot while leaving the smaller heel loose or the forefoot swimming. The real issue may be localized rather than a full-size difference.

Measure both feet

That sounds obvious, but many fit guides still ask customers to measure one foot and assume the other matches. We prefer left and right measurements separately so the difference is visible before production.