Figuring out whether a helmet will fit you can be tough when you’re shopping online. Thankfully, many brands offer size charts you can use to determine which size you should get. If you want to get really precise, you can measure the circumference of your head and compare it to the helmet circumference in the size chart.  Remember, you want a helmet that’s snug—but not too tight. And if you score an option with an adjustable fit system, you can always customize your fit once the helmet is on your head.