How to Measure Your Head for the Right Motorcycle Helmet Size
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The right helmet size starts with one simple measurement. A helmet that's too big can shift or even come off in a crash, and one that's too small gives you a headache in twenty minutes. Here's exactly how to measure your head for a motorcycle helmet, how to read a size chart, and how to know your size for sure.
Quick answer: how to measure for a motorcycle helmet
Wrap a soft tape measure around the widest part of your head, about 1 inch (2.5 cm) above your eyebrows and just above your ears, keeping it level all the way around. Read the measurement in centimeters, measure two or three times, and use the largest number. Match it to the helmet size chart. If you land between two sizes, choose the larger one.
What you'll need
- A soft, flexible tape measure (a tailor's or sewing tape)
- A mirror, or a friend to help
- No tape? A piece of string or a phone charging cable and a ruler work too
How to measure your head for a motorcycle helmet, step by step
- Find the widest point. Place the tape about 1 inch above your eyebrows in front, just above the tops of your ears on the sides, and around the fullest part of the back of your head.
- Keep it level. Check in a mirror that the tape isn't tilted up or down. A tilted tape gives the wrong size.
- Pull it snug, not tight. The tape should lie flat against your head without squeezing.
- Read it in centimeters. Helmet size charts are most precise in centimeters. Write down the inches too.
- Measure two or three times and use the largest measurement.
How to measure your head by yourself
Stand in front of a mirror and hold the end of the tape at the center of your forehead with one hand. Wrap it around with the other hand, check the mirror to make sure it's level, then read where the tape meets the start. With string: wrap it around your head the same way, pinch the point where it overlaps, and lay it flat against a ruler or tape measure.
Motorcycle helmet size chart
All GDM adult helmets use the same sizing and run true to size:
| Size | Head (cm) | Head (inches) | Hat size |
|---|---|---|---|
| S | 55–56 | 21 5/8–22 | 6 7/8–7 |
| M | 57–58 | 22 1/4–22 7/8 | 7 1/8–7 1/4 |
| L | 59–60 | 23 1/4–23 5/8 | 7 3/8–7 1/2 |
| XL | 61–62 | 24–24 3/8 | 7 5/8–7 3/4 |
| 2XL | 63–64 | 24 3/4–25 1/4 | 7 7/8–8 |
Youth sizes (for the GDM DK-630 Youth Motocross Helmet): Youth S 49–50 cm, Youth M 51–52 cm, Youth L 53–54 cm, Youth XL 55–56 cm.
Between sizes? Choose the larger size. Sizes differ between brands, so always check the chart for the helmet you're buying rather than going by the size of your old helmet.
How to know your helmet size if you can't measure right now
- Use your hat size. If you know your fitted hat size, the chart above converts it to a helmet size.
- Use the size finder. Every GDM helmet page has a "Find your size" tool, and our interactive size chart walks you through measuring.
- Check your current helmet as a starting point only. A size L in one brand can fit like an M or XL in another.
Common measuring mistakes
- Measuring too low across the eyebrows or too high on the forehead.
- Pulling the tape too tight, which puts you a size too small.
- Measuring over a hat or thick hair tie. Take them off first.
- Rounding down in inches. Use centimeters and the largest of your measurements.
Head shape matters too
Size is your head's circumference; shape is its outline seen from above. Most people have an intermediate oval head, slightly longer front to back than side to side, and GDM helmets are built for that shape. If you feel pressure on your forehead or the sides of your head even in the right size, read how to choose a helmet based on your head shape.
Check the fit when your helmet arrives
- It should feel snug all the way around, with firm, even pressure on your cheeks.
- There should be no painful pressure points, especially on your forehead.
- When you shake your head, the helmet should move with you, not slide around.
- With the chin strap fastened, you shouldn't be able to roll it off by pushing up at the back.
For the full fit test, see our motorcycle helmet fit guide. And if the size isn't right, exchanges are free within 30 days in the U.S.
Helmet sizing FAQ
How do I find my motorcycle helmet size?
Measure around the widest part of your head about 1 inch above your eyebrows, then match that number to the helmet's size chart. Choose the larger size if you're in between.
Should a motorcycle helmet be tight?
It should be snug, not painful. Expect firm pressure on your cheeks and even contact all around, with no hot spots. New helmets loosen slightly as the padding breaks in.
Is it better to size up or down on a motorcycle helmet?
If you're between sizes on the GDM chart, size up. Don't size up "just in case" if you're clearly in one size: a loose helmet is less protective.
Do I need a bigger helmet to wear a balaclava?
Usually not with a thin balaclava. Try the helmet on with it before a long ride.
Found your size? Shop motorcycle helmets, full face helmets or Bluetooth helmets.
