Never buy a used helmet or borrow someone else’s helmet. Over time the protective foam in helmets will adjust to the contours of a user’s head. A used or borrowed helmet may not offer as much protection as a new helmet.Please remember: Helmets will "break in" with use. It is important that the helmet fits as tight as one can comfortably withstand to wear.Wearing the wrong size helmet can increase your risk of serious injury or death in an accident. A helmet that is too large for your head may be dislodged or knocked off in an accident. To select the right size helmet for your head, follow these instructions:Measure your head. Wrap a tape measure around your head about one inch (2.5 cm) above your eyebrows.Use the sizing chart to select the helmet size that corresponds most closely to your head measurement. If your head size falls between two helmet sizes, try on the larger helmet first and then the smaller size. Try on the helmet by grasping both chin straps to pull the helmet completely onto your head, ensuring that the top of your head is in contact with the top of the helmet interior.Check for a proper fit. To make sure your helmet is the right size, check that the helmet inner lining fits snugly around your head, The top pad presses firmly on your head, The cheek pads contact your cheeks, and there is no space around your brow under the inner lining. Test this by trying to insert your fingers. If the helmet does not fit snugly, try on a smaller size.Test the helmet fit by placing your hands on each side of the helmet. While holding your head as motionless as possible, try rotating your helmet from left to right then up and down. If you can feel the helmet padding sliding on your head, it is too big, try a size smaller. You should feel the helmet move the skin on your head and face as you try to move the helmet.Fasten the retention system (chin strap) as tight as possible under your jaw without causing pain. There must be no slack in the strap, and the strap must be tight up against your jaw.Test the retention system (chin strap). Put your hands on the back of the helmet and try to push the helmet off by rotating it forward. Put your hands on the front of the helmet above your forehead (or on the chin guard) and try to push the helmet off by rotating backward. If helmet comes off, try another size or another model or brand. Repeat steps 3 through 8 until you find a helmet that fits your head snugly and securely.HJC AR-10 III Sizing:SIZECENTIMETERHAT SIZEINCHESXS54-556 3/4 – 6 7/821 1/4 – 21 5/8S56-577 – 7 1/822 – 22 1/2M58-597 1/4 – 7 3/822 7/8 – 23 1/4L60-617 1/2 – 7 5/823 5/8 – 24XL62-637 3/4 – 7 7/824 3/8 – 24 3/4XXL64-658 – 8 1/825 1/4 – 25 5/8Impact Sizing:Klim Sizing:SIZECENTIMETERS55-56M57-58L59-60XL61-62XXL63-64HJC CS-R3 Sizing:SIZECENTIMETERHAT SIZEINCHESXS54-556 5/8 - 6 3/420 7/8 - 21 1/4S55-566 7/8 - 721 5/8 - 22M57-587 1/8 - 7 1/422 1/2 - 22 7/8L58-597 3/8 - 7 1/223 1/4 - 23 5/8XL60-617 5/8 - 7 3/424 - 24 3/8XXL62-637 7/8 - 824 3/4 - 25 1/4HJC CL-17 Sizing:SIZECENTIMETERHAT SIZEINCHES3XL65-668 1/8 - 8 1/425 5/8 - 264XL67-688 3/8 - 8 1/226 3/8 - 26 3/45XL69-708 3/427 1/4 - 27 5/8HJC CL-Y Youth Helmet Sizing:SIZECENTIMETERHAT SIZEINCHESYouth S49-506 1/8 - 6 1/419 1/4 - 19 3/4Youth M51-526 3/8 - 6 1/220 - 20 1/2Youth L53-546 5/8 - 6 3/420 7/8 - 21 1/4HJC CS-5N Size ChartXSSMLXL2XLHelmet Size (cm)54-5555-5657-5858-5960-6162-63Cheek Pad (mm)454035403530Liner Size (mm)1512915129G Force Sizing:Helmet SizeCentimeter 2XS51-52XS53-54S55-56M57-58L59-60XL61-622XL632XL63+Pyrotect Sizing:Helmet SizeInchesHat SizeCentimeters Junior- XXXS, XXXS, XS19 1/4 - 20 1/86 - 6 1/4 49-51XX Small20 - 21 1/46 3/8 - 6 1/251-52X Small20 3/8 - 21 1/86 5/8 - 6 3/452-54Small21 1/4 - 226 3/4 - 7 1/855-56Medium22 1/2 - 22 7/87 1/8 - 7 1/457-58Large23 1/4 - 23 5/87 3/8 - 7 1/258-60X Large24 - 24 3/87 1/2 - 7 3/461-62XX Large24 3/4 - 25 1/87 3/4 - 863-64XXX Large25 1/4 - 25 1/28 1/4 - 8 1/265-66