Sizing a motocross helmet starts with a soft tape measure around the widest part of your head, matched against the brand’s own chart.
Two riders with the same head measurement can land in completely different sizes, because Fox Racing and Bell each publish their own fit tables. So skip the generic wall chart, measure your head in centimeters, and compare that number to the motocross helmet size chart published by the exact model you plan to buy.
Only three honest steps come between that number and a helmet that fits: measure, compare, and verify on your head. Every brand chart you will see relies on the same head circumference, so getting that first measurement right settles most fit problems before you order.
How Do You Measure Your Head For A Motocross Helmet?
Wrap a flexible measuring tape around the widest part of your skull and write the number down in centimeters. That circumference is the value every brand chart keys on, so take the measurement twice and use the one that repeats.
- Position the tape just above your eyebrows and ears, circling the widest point of the head.
- Keep the tape level and snug — flat against your hair, never pulled tight or angled upward.
- Read the number in centimeters and measure again; if the two passes differ, go with the larger one.
Most adult heads fall between 53 and 64 cm, which is exactly the range the Fox and Bell charts cover. Compare your measurement to a chart that matches the helmet’s brand and model, not a generic one taken from another product.
Why Do Motocross Helmet Size Charts Vary By Brand?
The short version: manufacturers use different shell molds, liner thicknesses, and size labels, so the same centimeter reading can map to different letters.
| Fox Racing Size | Head Circumference (cm) | Head Circumference (in) |
|---|---|---|
| XS | 53–54 | 20.9–21.3 |
| S | 55–56 | 21.7–22.0 |
| M | 57–58 | 22.4–22.8 |
| L | 59–60 | 23.2–23.6 |
| XL | 61–62 | 24.0–24.4 |
| 2X (XXL) | 63–64 | 24.8–25.2 |
Those parts are model-specific, so use that model’s own chart rather than a general one.
The Fit Test No Size Chart Can Replace
A size chart gets you to the right neighborhood; the helmet on your head makes the final call. It should feel snug and even all around, with no painful pressure points anywhere.
- Slide it on without forcing; it should sit level, with your eyes centered in the eye port.
- Press around the crown, forehead, and temples: even pressure is fine, but a sharp hot spot is not.
- Shake your head and grip the chin bar; if the shell shifts or rocks, it is too loose.
- Cheek pads should press your cheeks lightly without pushing your jaw.
Never choose by hat size alone unless the brand’s chart explicitly shows hat-size conversions — Bell’s does, but not every chart does. Keep youth helmets on their own charts too; youth and adult ranges are not interchangeable. And when you later replace liners, cheek pads, or accessories, order by the exact helmet model and its official chart.
Once your measurement and the test fit agree, the search narrows to the helmet itself. Our guide to the best adult motocross helmets compares tested models by shell, ventilation, and price, so you don’t have to start that research from zero.
One last rule: if a shell feels borderline loose when new, padding only compresses with time. A snug, even fit on day one is the one worth paying for.
FAQs
Should I round up if my head lands between two listed sizes?
Try both neighboring sizes if you can. A motocross helmet should sit with even, snug pressure and no hard spots, so when your measurement lands between ranges, the size that presses evenly without hurting is the correct one. A shell that rocks or shifts when you move your head is dangerous, so do not choose a loose fit to gain comfort.
Can I use my hat size to pick a motocross helmet?
Centimeters are the reliable answer. Hat sizes are only safe when the manufacturer’s chart explicitly includes a hat-size conversion, the way Bell Racing’s guide does. Charts without one use a different scale, and guessing invites a sloppy shell. Measure around the widest part of your head and compare that number to the exact brand and model.
Will a new motocross helmet stretch out?
Pads settle slightly over the first rides, but not enough to fix a bad fit and not overnight. Foam liners compress slowly. A new motocross helmet should feel snugly comfortable at purchase. If it presses sharply at any point when new, try another size or another model rather than expecting it to break in.