Ahh, but the question is how do you know if it fits you?
First put the thing on and adjust the buckles making sure that you can slip 1 finger between the strap and your chin and the V shape part of the straps on both sides of your head are just slightly under and front of the ears.
Now try moving the helmet from side to side and front to rear to see if it could come off if it weren't for the straps. If if feels like it could come off then the helmet is not the right fit go to another size or a different brand.