i wear a large in almost every helmet i have owned. 23 1/2" noggin.

i have a large exo 100, and it fits snugly. not painful, but just about perfect.

the helmet shell on the exo 100 scorpion is not the same size throughout the range of xs - xxl. -- read on.

the large size shell, the helmet itself is noticeably larger than the small that i purchased for my wife, and kids. they have 22" heads.. almost all the same, between 22, and 22 1/4. the small fits them well.

the xs-s-m shells appear to be one size, and the l-xl-xxl appear to be the a larger size shell.

additional liners can be purchased to fit these shells. i have ordered a M and a XL liner for 13.95 each. my son and I go from crew cut to mop hair throughout the year, so i want the option to change size a bit.

ps--- the zip in skirt/ ear cushions have a size range listed on them that appears to echo what i have written. one skirt reads xs/s/m, and the other reads l/xl/xxl.

i hope that this information will help someone down the line.

robbie, NY