A helmet should fit your head shape, stay securely in place, and meet the safety requirements where you ride. Measure your head according to the manufacturer’s instructions, then use the size chart as a starting point rather than a final answer. Helmet shapes vary, so two helmets marked with the same size may feel quite different. Try several models from reputable makers and look for applicable certification labels required in your region.
With the helmet fastened, the liner should feel evenly snug without painful pressure points. Move the helmet gently from side to side and front to back; your skin should move with the fit rather than the shell shifting freely. Check that it does not roll off when you follow the manufacturer’s fit guidance. Wear it for several minutes to notice emerging discomfort. A new liner may settle slightly, but a helmet should not depend on painful pressure to stay secure.
Confirm that the chin strap closes correctly and that you can operate the visor and vents with your gloves on. If you wear glasses, test them with the helmet in place. Follow the maker’s care and replacement instructions, and replace a helmet after an impact if advised, even when visible damage is absent. Avoid altering the shell or liner, and do not buy a used helmet with unknown impact or storage history. Fit, condition, and proper fastening all matter.