Our sizing is based around average, reasonably fit people. It should match the size you'd choose on the high street, not a cycling racing brand. Brands tend to have wildly varying size policies. Ours is "real".

CIRCUMFERENCE <57cm 57-61cm >61cm

Measure horizontally around the widest part of your head, above your ears
A quick tip... most people think they have a large or a small head, but we find almost everyone is a medium. Years of experience. Promise!