A helmet's safety rating only matters if the helmet actually fits. An expensive helmet worn loose or tilted back offers less real protection than a well-fitted budget one, so fit should be the first thing you check, not the last.
Measuring your head
Wrap a soft tape measure around the widest part of your head, roughly an inch above your eyebrows, and check that measurement against the manufacturer's size chart — sizing varies between brands, so don't assume your size carries over. Most adult helmets come in a small range of shell sizes with an adjustable internal fit system to dial in the final fit.
Checking the fit
A properly fitted helmet sits level on your head, about one to two finger-widths above your eyebrows — not tilted back off your forehead. The side straps should form a V just under your ears, and the chin strap should be snug enough that you can fit one or two fingers between it and your chin, no more. Once adjusted, the helmet shouldn't shift when you shake your head side to side or nod up and down.
When to replace a helmet
Helmets are designed to absorb a single significant impact by deforming — once that happens, the helmet needs to be replaced even if the damage isn't visible. Most manufacturers also recommend replacing a helmet every few years as the materials age, even without a crash, since UV exposure and general wear can affect how the foam performs.
Browse fit options in our Cycling Helmets & Protection collection.