Determine Your Size
To determine the correct size, you need to measure the circumference of the head. To do this, wrap a tape measure around the head, keeping the tape just above the ears and level from front to back. Once you’ve determined the correct measurement, you can select a helmet in the correct size or size range using the size chart below as a guide.
Put the Helmet On
Start by putting the helmets on and checking to make sure the helmet fits comfortably and securely. Helmets with a fit/stability system should fit with just a little room between your head and the headband when the fit system is loose. If it does not, you should replace it with one that does. Helmets without a fit/stability system (pads only, such as a full-face helmet) should fit snugly but comfortably.
Once on and adjusted, a helmet should fit snugly on the head so that the skin on the forehead moves slightly when the helmet is moved back and forth. It should not cause a headache or be uncomfortably tight.
You should always wear the helmet positioned low enough in the front to protect your forehead, but not so low that it hinders your vision. A space of approximately 1 inch/2.5cm between the edge of the helmet and your brow is a good reference.