Helmet Size Guide
A helmet only protects you if it fits. Too loose and it can shift or come off in a crash; too tight and you'll get headaches and pressure points within twenty minutes. The good news: getting the right size takes two minutes and a soft tape measure.
Step 1: Measure your head
- Use a cloth or soft measuring tape (a phone charging cable and a ruler works in a pinch).
- Wrap it around the widest part of your head: about 1 inch above your eyebrows, just above your ears, and around the back of your head.
- Pull it comfortably snug, read the number, then measure again. Use the larger of the two measurements.
Step 2: Find your size
GDM Adult Helmet Size Chart
| Size | Inches | Centimeters | Hat size |
|---|---|---|---|
| Small | 21 5/8" – 22" | 55 – 56 cm | 6 7/8 – 7 |
| Medium | 22 1/4" – 22 7/8" | 57 – 58 cm | 7 1/8 – 7 1/4 |
| Large | 23 1/4" – 23 5/8" | 59 – 60 cm | 7 3/8 – 7 1/2 |
| X-Large | 24" – 24 3/8" | 61 – 62 cm | 7 5/8 – 7 3/4 |
| XX-Large | 24 3/4" – 25 1/4" | 63 – 64 cm | 7 7/8 – 8 |
Applies to GDM Venom, Ghost, Demon, Beast, Rebel, Renegade and DK-140 helmets.
GDM Youth Helmet Size Chart
| Size | Inches | Centimeters | Hat size |
|---|---|---|---|
| Youth Small | 19 1/4" – 19 3/4" | 49 – 50 cm | 6 1/8 – 6 1/4 |
| Youth Medium | 20" – 20 1/2" | 51 – 52 cm | 6 3/8 – 6 1/2 |
| Youth Large | 20 7/8" – 21 1/4" | 53 – 54 cm | 6 5/8 – 6 3/4 |
| Youth X-Large | 21 5/8" – 22" | 55 – 56 cm | 6 7/8 – 7 |
Applies to the GDM DK-630 Youth Motocross Helmet.
In between two sizes?
Go with the smaller size if the fit test below feels snug but not painful. A new helmet's liner and cheek pads compress a little over the first several rides, so a helmet that feels slightly tight in the box usually settles into a perfect fit. A helmet that feels roomy on day one only gets looser.
Step 3: Check the fit when it arrives
- Snug all around. The helmet should feel firm against your cheeks and the top of your head, with no gaps at your forehead.
- No hot spots. Wear it for 15–20 minutes indoors. A sharp pressure point on your forehead or temples that leaves a red mark means it's too small or the wrong shape for your head.
- The shake test. With the strap fastened, shake your head side to side and up and down. The helmet should move with your head, not slide around on it.
- The roll-off test. Fasten the strap, grab the back of the helmet and try to roll it forward off your head. If it comes off or slides over your eyes, it's too big.
- Eyes centered. Your eyes should sit in the middle of the eye port, with the brow of the helmet just above your eyebrows.
Please do these checks indoors, before riding, and keep the helmet clean and the tags on until you're sure. Under our 30-day return policy, items need to be unworn, unused and in their original packaging to be returned.
Replacement liners and cheek pads
If your helmet has loosened up after a lot of miles, you don't always need a new helmet. We carry replacement GDM helmet liners and cheek pads in every size.
Still not sure?
Call us at 818-495-5291 or email info@motorcyclehelmetoutlet.com with your head measurement and the helmet you're looking at, and we'll help you pick a size. Ready to shop? Browse all DOT-approved motorcycle helmets, with free USPS shipping on every order.