HOW TO DETERMINE HELMET SIZE
To find the proper helmet size, use a flexible tape measure and wrap it around the largest portion of your head. Your starting point should be approximately 1 in. above your eyebrows. Gently guide the tape measure around your head. Make sure you measure the fullest portion of your head. Once you find the measurement, use this number to determine your size helmet.
For example, the Limar UltraLight + helmets come in two sizes: Medium (53-57 cm / 19.7"-22.4"); Large (57-61 cm / 22.4"-24"). (The average adult male has a head circumference of 57 cm. ) Select the size that gives you a little extra room to make adjustments using the retention system to find the most comfortable yet secure fit. You do not want the helmet to be too tight. On the other hand, you do not want the helmet to be too loose so it slips while riding.
TIP: If you measured your head and came up with 57 cm, you may want to go with the size large so you have more adjustment room for summer or winter head accessories.