How to Measure for a Dirt Bike Helmet | One Tape Gets The Right Fit

Measuring for a dirt bike helmet requires a soft tape measure placed about one inch above the eyebrows and ears, wrapped around the widest part of the head, then matched to the manufacturer’s specific size chart — because sizing varies by brand and model.

A helmet that shifts forward or slides when you look up is worse than no helmet at all — it’s a false sense of protection. The fix starts with one number: your head circumference, measured correctly. Whether you’re buying your first full-face or upgrading, the process is the same across brands. Here’s the exact method, the common mistakes that ruin the fit, and what to check after the helmet is on.

The Only Measuring Method That Works For Any Dirt Bike Helmet

Use a soft cloth measuring tape — the kind a tailor uses. If you don’t have one, grab a non-stretchy string or shoelace and a ruler. Place the tape about one inch above your eyebrows in front and at the widest point at the back of your head — typically just above the ears. Keep the tape level all the way around, snug but not tight enough to compress the skin. Take the measurement in both inches and centimeters, and repeat twice. If the numbers differ, use the larger one. If you plan to wear a balaclava or head sock under the helmet, measure with it on — that half-inch of fabric changes the fit.

Matching Your Measurement To The Right Size

This is where most people go wrong: head circumference is universal, but helmet sizes are not. A “Large” in one brand can feel like a “Medium” in another. You must use the manufacturer’s own size chart for the specific model you’re buying. For example, Bell Helmets publishes a chart that starts at XS for 53–54 cm (20 7/8–21 1/4 inches), with each size stepping up roughly 2 cm. Bell Racing USA’s guidance directs you to that same chart, not to a generic size table. The measurement you took is the key; the brand’s chart tells you which lock to open it with.

Four Fit Checks To Run Before You Buy

The measurement is just the first gate. A helmet that measures right can still fit wrong. After you match your number to the chart and put the helmet on, run these checks:

• Forehead protection. The helmet should sit low enough to protect your brow without pushing up your vision. If you can see the brim edge when you look up, it’s too high.
• Cheek and crown pressure. The cheek pads should press firmly against your face — no space to slip a finger between the pad and your cheek. The crown should feel snug without a single pressure point. If you feel a hot spot, that helmet’s shell shape doesn’t match your head.
• The roll test. With the chin strap fastened, try to roll the helmet forward off your head. If it moves, it’s too loose. A properly fitted helmet should not shift front-to-back at all.
• The finger test. You should not be able to fit a finger between the back of your head and the rear padding, between the front padding and your forehead, or under the cheek pads. If you can, go down a size or a shell shape.

Fitting A Dirt Bike Helmet: The Final Steps

Once the helmet passes all four checks and you’re ready to buy, check our tested roundup of the best dirt bike helmets to see which models match your head shape and budget. Two last things: never buy a helmet that fits only when the retention system is cranked tight — a helmet that requires tightening to feel snug is too big. A helmet that fits correctly the first time is the one you’ll actually wear — and that’s the whole point.