A dirt bike helmet is sized by measuring your head circumference about one inch above the eyebrows and ears, then matching that measurement to the specific brand’s size chart and verifying a snug, even fit with the chin strap fastened.
For the full breakdown, see our best White Dirt Bike Helmet guide.
Getting the right dirt bike helmet size takes about two minutes. An improperly fitted helmet can shift during a ride or compromise protection. You need only a soft measuring tape or a piece of string.
How to Measure Your Head for a Dirt Bike Helmet
Wrap a cloth tape level around the widest part of your head, roughly one inch above your eyebrows and just above your ears. This captures the largest circumference. Write down the measurement in centimeters or inches.
Matching Your Measurement to a Size Chart
| Size | Head Circumference (cm) | Head Circumference (in) |
|---|---|---|
| XS | 53–54 | 20 7/8–21 1/4 |
| SM | 55–56 | 21 5/8–22 |
| MD | 57–58 | 22 1/2–22 7/8 |
| LG | 59–60 | 23 1/4–23 5/8 |
| XL | 61–62 | 24–24 1/2 |
| 2XL | 63–64 | 24 7/8–25 1/4 |
Trying on both is safest.
Fit Checks That Confirm the Right Size
Fasten the chin strap and run through these checks:
- Snug feel, not pain. Even pressure across cheeks and top of head without pressure points. Cheek pads should press firmly — if they don’t, the helmet is too wide.
- Minimal movement during shake tests. Shake head side to side and up and down. Helmet should stay with your skin, not slide independently.
- No gap behind the back of the head. You should not easily slide fingers between helmet and skull.
- Level position. Front edge about one inch above eyebrows, not blocking upward vision.
- Push and twist test. Push from back — helmet should not roll forward. Twist with both hands — your head should turn with it.
If you pass all checks, the helmet is likely the right size.
Common Sizing Mistakes to Avoid
FAQs
References & Sources
- NHTSA. “Fitting a Helmet” (PDF) Outlines measurement and fit-test procedures for motorcycle and bicycle helmets.
- Bell Racing USA. “Bell Helmet Size Guide” Provides official measurement instructions and size chart for Bell dirt bike helmets.