Measure your head circumference to find your helmet size

A helmet only protects you if it stays on your head during a crash. The first step is measuring around your head at the widest point — usually about an inch above your eyebrows and ears. Use a soft measuring tape (the kind tailors use) or a piece of string you can measure afterward with a ruler. Wrap it snugly but not so tight that you can't breathe, and write down the number in centimeters or inches.

Most helmet brands size by centimeters. A measurement of 52–55 cm is typically a small, 55–58 cm is medium, 58–61 cm is large, and 61–64 cm is extra-large. Check the specific brand's sizing chart before you buy, because some manufacturers run small or large. If your measurement falls between two sizes, choose the larger one — you can adjust the fit with the helmet's internal padding.

Key Takeaways

  • Measure the circumference of your head about an inch above your eyebrows using a soft tape measure, and compare that number to the helmet brand's sizing chart.
  • The helmet should sit level on your head, covering your forehead, with the front edge one to two finger-widths above your eyebrows.
  • The chin strap must be snug enough that you can fit only one finger between the strap and your chin when it is fastened.
  • Shake your head side to side and forward and backward — the helmet should not shift or rotate, and your vision should not be blocked.
  • Most helmets have removable padding that you can swap out to fine-tune the fit if the helmet is slightly loose.

Position the helmet level on your head

Once you have the right size, put the helmet on and position it so it sits level — not tilted back or forward. The front edge should be one to two finger-widths above your eyebrows. If the helmet tips back and exposes your forehead, or tips forward and blocks your vision, the size is wrong or the padding needs adjustment.

Look in a mirror and check that the helmet covers the sides of your head evenly. The back should not sit so high that it leaves the back of your neck exposed, and it should not sit so low that it pushes down on the back of your head uncomfortably. If padding is bunching up or creating gaps, you may need to add or remove foam pads from the interior.

Fasten and tighten the chin strap correctly

The chin strap holds the helmet in place during a fall. Thread the strap under your chin and fasten the buckle — most modern helmets use a click-lock or magnetic closure. The strap should be snug enough that you can fit only one finger between the strap and your chin when it is fastened. If you can fit two fingers, tighten it. If you cannot fit any finger, loosen it slightly.

Make sure the strap does not twist or bunch as it runs from the helmet to the buckle. The two sides of the strap should form a V-shape under your chin, not a straight line or a twisted loop. A twisted strap can slip during impact and let the helmet rotate off your head.

Test the fit by moving your head

Shake your head side to side and forward and backward. The helmet should not shift, rotate, or slide in any direction. If it moves, the size is too large, the chin strap is too loose, or the padding is not seated correctly. Try tightening the chin strap first, then check the padding fit.

Look straight ahead, then look down and to each side. Your vision should not be blocked by the helmet's edges or padding. If you cannot see clearly, the helmet may be positioned too far forward or the padding may be too thick in the front. Adjust the position and try again.

Adjust or replace the interior padding

Most helmets come with removable foam pads glued or velcroed to the inside. If the helmet is slightly loose after you have tightened the chin strap, you can add thicker padding to the crown (top) or sides. Many brands sell replacement pad kits in different thicknesses.

If the helmet is too tight, you can remove some padding, but do not remove so much that the helmet becomes loose. A helmet that moves on your head offers less protection than one that fits snugly. If adding or removing pads does not solve the problem, the helmet size is wrong and you should try a different size.

Know when to replace your helmet

A helmet that has been in a crash should be replaced, even if it looks fine on the outside. The foam inside compresses during impact and loses its ability to absorb energy. Cracks in the shell, dents, or loose padding are also signs that a helmet should be retired.

Helmets also degrade over time from sun exposure and sweat. Most manufacturers recommend replacing a helmet every three to five years, depending on how often you ride and how you store it. Keep your helmet out of direct sunlight and heat when you are not wearing it, and wash the padding with mild soap and water to extend its life.

Frequently Asked Questions

What if my head is between two helmet sizes?

Choose the larger size. You can add padding inside to make it fit snugly, but you cannot make a small helmet bigger. Start with the thicker pads that come with the helmet, and buy additional pads if needed.

Can I wear a helmet over a hat or hood?

No. A hat or hood changes the shape of your head and throws off the fit. The helmet will not sit level or stay in place during a crash. Wear a helmet directly on your head, or choose a helmet with good ventilation if you are worried about cold or sun.

How tight should the chin strap really be?

Tight enough that you can fit one finger between the strap and your chin. If the strap is too loose, the helmet can rotate or slide off during a fall. If it is too tight, it can cut off circulation or cause discomfort on long rides.

Do I need to replace my helmet if I fell but did not hit my head?

If the helmet itself hit the ground or another object, replace it. The foam inside may have compressed even if you did not feel impact. If you fell but the helmet did not make contact, you can keep wearing it.

Why does my helmet feel loose even though the chin strap is tight?

The padding may have compressed or shifted, or the helmet size may be too large. Try repositioning the padding inside the helmet, or add thicker pads to the crown and sides. If that does not work, try the next smaller size.