The Lifer helmet is available in 3 different shell sizes to accommodate different size heads.  We size each individual helmet shell up and down by thinning and thickening the sizing liners to get a perfect fit for everyone. Depending on what size range your head lands in once you've measured your head will determine which Lifer Helmet will be the best fit for you. For an even more accurate fit you can combine different size back and front sizing liners to customize your helmet fit to your specific head shape and size.