How to Size & Fit Your Helmet

Using a long strip of paper, have a friend measure horizontally around the largest part of your head, about an inch above your eyebrows (see illustration). Measure the length of the strip with a ruler and use the following chart to determine your hat and helmet size:

Helmet Size(strip length) Inches Centimeters Cheek Pads (Arai)
Small(6 7/8"-7") 21 5/8" - 22" 55 - 56 15mm
Medium(7 1/8"-71/4") 22 3/4" - 23" 57 - 58 20mm
Large(7 3/8"-7 1/2") 23 1/8" - 23 1/2" 59 - 60 25mm
X Large(7 5/8"-7 3/4") 24" - 24 3/8" 61 - 62 30mm

If you have any questions about sizing, ordering, or how your helmet should fit after you have received it, please give us a call at 800-222-1994 or email

Helmet Fit Considerations:

For safety, comfort, and noise reduction, your helmet should fit snugly. If you can rotate your head inside the helmet, it's too loose. Helmets have a layer of soft foam comfort 'upholstery' that covers the hard polystyrene (styrofoam) impact absorbing lining. You should be able to feel each pad pressing against your head. If you hold the helmet isometrically (one hand on each side of the helmet) and try to move your head inside of the now 'stationary' helmet with only your neck muscles, you should feel the soft foam upholstery compressing between your skull and the polystyrene. If you do not feel any compression, your head will be right up against the unyielding polystyrene. The helmet padding will break in and soften during about the first ten hours of wear, so if it feels a bit too snug when new, that's normal. A helmet should be snug... not uncomfortable or over-tight.


Arai Vector 2 (#1379) / Arai XD4 (#1388)


Head Shape & All Day Fit

A good fitting helmet is a safer, quieter helmet. To fit any helmet properly you should position it on your head so the top of the eye port opening is about one finger width above your eyebrows. This will tell you if the chinbar fits the shape of your jaw, and how the cranial section fits your head. Pay special attention to the fit around the crown of your head (the part that is contacted by a baseball cap's band). Sizing the helmet to better fit the face instead of the head, will result in a looser fitting, noisy helmet.

Different helmets fit wide, narrow, round, square and oval heads differently (nothing yet for pinheads). The "Long Oval" is very long front-to-back, and narrow side-to-side, offering additional forehead room for those who find that most helmets have pressure points in the forehead. The "Intermediate Oval" is a little shorter front-to-back and a little wider side-to-side than Long Oval. The "Round Oval" is even a little shorter front-to-back and a little wider side-to-side than Intermediate Oval. These shape differences are part of the rigid EPS liner, not the soft upholstery. Only Arai offers these specific head shapes to give you a perfect all day, everyday fit. Sometimes you'll need to try several models to find what matches your head shape best. If your new helmet does not fit or feel 'right,' please send it back for a size/model exchange, or refund.