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This information and other SafeCyclist Teacher Master Pages are available as PDF downloads on our Educational Resources page.
Bicycle helmets come in standard sizes to fit heads with different circumferences. A bicycle helmet that doesn’t fit or isn’t adjusted properly is not safe. The size you need depends on the circumference of your head.
Compare the circumference of your head to the chart below to determine what size your helmet should be. Your helmet should fit snugly, so use the different thickness pads that come with your helmet to adjust the fit. Helmets are standardized but heads are not, so you’ll want to use the right combination of thick and thin pads in front and back or on the sides to make sure your helmet fits your head in all directions. Many helmets also come with a twistable adjuster at the back to achieve the correct snugness on your head.
Your helmet should be flat on your head and you should be able to see the front of the helmet just at the top of your vision. Having trouble getting it right? Put two fingers over your eyebrows; your helmet should rest just on top of your fingers. Any higher up and it isn’t sitting flat on your head—bring the front of the helmet further down. (If you’ve never had a properly adjusted helmet before, it will feel a bit weird at first.)
The side adjustment buckles should form a “V” shape under, and slightly in front of, your ears. When properly fitted, your helmet should not be able to be pushed backwards or forwards.
Always buckle the strap under your chin. The chin straps should be buckled and checked for tightness on every ride. It should be snug but not uncomfortably tight. Open your mouth wide—you should feel the strap tugging on the helmet.
Check for fit
With the helmet correctly positioned on your head, gently rotate the helmet from left to right and from front to back without moving your head. If the skin on your forehead moves with the helmet, then the fit is correct.
If your helmet easily slides across your forehead, then it is too loose. Take it off and adjust the pads inside, or twist the adjuster at the back to tighten it up so it can protect you in the event of a crash.
Replace a helmet after a crash
The impact of a crash will crush the foam inside your helmet, even if you can’t see any damage.
Always replace a helmet after crashing in it, because it will lose its ability to protect your head next time.