Helmet Size Between Two Sizes: Should You Size Up or Down?
If your head measurement falls between two motocross helmet sizes, size down. A helmet that starts slightly snug will break in to your head shape within the first few rides as the EPS liner and comfort foam compress and conform. A helmet that starts slightly loose will only get looser, and a loose helmet doesn't protect you the way it was designed to.
Why You Almost Always Size Down
A properly fitting helmet should feel snug, not tight. Snug means even pressure across your forehead and the sides of your head without pressure points that cause pain. When you first put on a new helmet that fits correctly, it should require some effort to pull on over your head. The cheek pads should press firmly against your cheeks. Within five to ten rides, the comfort liner will compress to match your head shape, and that initial snugness will ease into a precise, custom-feeling fit.
If you size up when you're between sizes, the helmet will feel immediately comfortable out of the box. That's actually a warning sign. Comfortable from the first moment usually means there's already too much space. As the liner compresses through use, that space increases. A helmet with extra room can rotate independently of your head in a crash, which reduces its ability to manage impact forces correctly.
Helmet brands design their size ranges with a break-in margin built in. Sizing down is the intended use case when you're on the border.
The Fit Test That Confirms the Right Size
Don't rely on the size chart alone. After you pull the helmet on, run through these checks:
- The roll test. Grab the back of the helmet with both hands and try to roll it forward off your head. If it rolls off, it's too big. If it stays put and takes your skin with it, the fit is correct.
- The cheek pad check. Press your fingers against your cheeks through the helmet opening. You should feel firm resistance from the cheek pads. If you can easily slide your fingers behind the pads, the helmet is too large.
- No rotation. Turn your head left and right. The helmet should move with your head, not after it.
- Even pressure, no hot spots. Pressure should be distributed evenly across your forehead and the sides of your skull. Localized pressure on any single point means the helmet's shape doesn't match your head shape, which is a fit issue that sizing won't fix.
- No gaps at the brow. Look in a mirror and check that the front rim of the helmet sits about one to two finger-widths above your eyebrows with no daylight gap at the forehead.
The BTO sizing guide has brand-specific charts and measurement instructions. Use it to confirm your baseline measurement, then apply the roll test and cheek pad check to validate the actual fit in whichever size you order.
When Sizing Up Makes Sense
Sizing up is the right call in two situations. First, if the smaller size creates sharp, painful pressure points after five minutes that don't ease up, the shell shape is wrong for your head shape, and no amount of break-in will fix a structural mismatch. In that case, try a different brand rather than sizing up, since the issue is head shape, not size.
Second, if you have a genuinely wide or high-volume head and the smaller size creates a vice-grip feeling across the temples even after extended wear, the larger size may be more appropriate. But confirm this with the roll test. If the larger size fails the roll test, go back to the smaller size and evaluate different brands with wider shell geometries.
For more on how head shape affects helmet fit across brands, read the helmet head shape guide. Round oval, intermediate oval, and long oval heads fit differently in the same size, and choosing a helmet built for your head shape resolves most between-size fit issues before they start.
Youth Helmets: The Same Rule Applies
For youth riders, the same sizing-down principle holds. The temptation to buy a youth helmet with growing room is understandable, but a loose helmet is a liability, not an investment. If your child's head measurement falls between youth sizes, go with the smaller size. For a full breakdown of youth helmet sizing including measurement instructions and a size chart by age range, see the youth motocross helmet size guide.
Common Mistakes When Sizing Helmets
- Measuring over hair. Measure your bare head circumference at the widest point, one finger-width above your eyebrows. Thick hair adds a centimeter or more to the measurement and will push you toward the wrong size.
- Trusting comfort without testing. Immediate out-of-box comfort often signals a loose fit. Always run the roll test.
- Comparing sizes across brands. A medium in Fox is not the same as a medium in Bell or Alpinestars. Always check the brand-specific chart for the helmet you're buying.
- Skipping the cheek pad check. Cheek pads are the most important retention contact point in most motocross helmets. If they're not firm, the helmet won't stay in position during impact.
Bottom Line
Between two sizes: size down. Confirm with the roll test and cheek pad check. If the smaller size causes sharp pressure points after extended wear, evaluate a different brand with a shell shape that matches your head geometry rather than sizing up. A helmet that fits correctly from day one, even if it feels snug at first, is the one that will actually protect you.
Browse the full motocross helmet collection at BTO Sports. If you need help narrowing down sizes or comparing brands, the BTO help center is available for fit questions before you order.
Back to Fit + Function FAQs.