I just started printing this last night. From reading everything here it appears the maker wears a 59cm motorcycle helmet that is snug. My measurement for the same type of motorcycle helmet would be 58cm. So using that and the one image I found with a few measurements for "A" size of this helmet I think 101% should be just right for me leaving a little room for some foam to make it comfortable. Once its all printed I will give all my measurements for sizing.