Helmet sizing is one of the few measurements in motorcycling that doesn't tolerate a guess. A shell that's a size too large will rotate on impact and won't sit where the energy management foam expects it to. A shell that's a size too small will deform your day before it ever sees a crash. The good news: it takes about ninety seconds and one piece of equipment to get it right.
What You'll Need
- A soft cloth tape measure — the kind tailors use. Not a steel construction tape
- A mirror, or a friend with two working hands
- A pen and something to write on
- Two minutes
No soft tape? Wrap a piece of string or a phone-charging cable around your head as described below, mark it with a pen, then lay it flat against a ruler. Less elegant, same number.
Where to Measure
You're measuring the maximum circumference of your head. The tape runs roughly one finger's width above your eyebrows at the front, around the widest point at the back — usually the small bump at the base of the skull called the occipital ridge — and back to the start. Not over the ears. Not across the temples on a downward slant.
Step by Step
- Set your hair. Brush it flat — anything you wouldn't ride with shouldn't be there during the measurement. Take off hats, headbands, and earbuds.
- Find the front anchor. Place the start of the tape on your forehead, about one finger's width — roughly 2 cm — above your eyebrows.
- Wrap horizontally. Take the tape around your head, keeping it level. The back of the tape should cross the widest point at the rear of your skull, not slope down toward your neck.
- Pull snug, not tight. The tape should sit firmly against the skin without compressing it. If your skin puckers, you've gone too far.
- Read the number. In centimetres if you can — helmet sizing charts are almost all metric. Write it down.
- Do it twice more. Three measurements, take the largest. Heads don't change between readings; tape positions do.
Convert to Helmet Size
The sizing below is the consensus across most major manufacturers — Shoei, Arai, AGV, HJC, Bell, and Schuberth all hover within a centimetre of these ranges. Always confirm against the specific brand's chart, because shell shapes and internal padding vary, and you may end up between sizes on one brand and squarely in the middle of another.
| Size | Centimetres | Inches | Hat Size (US) |
|---|---|---|---|
| XS | 53 – 54 cm | 20.9 – 21.3" | 6 ⅝ – 6 ¾ |
| S | 55 – 56 cm | 21.7 – 22.0" | 6 ⅞ – 7 |
| M | 57 – 58 cm | 22.4 – 22.8" | 7 ⅛ – 7 ¼ |
| L | 59 – 60 cm | 23.2 – 23.6" | 7 ⅜ – 7 ½ |
| XL | 61 – 62 cm | 24.0 – 24.4" | 7 ⅝ – 7 ¾ |
| 2XL | 63 – 64 cm | 24.8 – 25.2" | 7 ⅞ – 8 |
Between two sizes? Go with the smaller one. Helmet padding compresses a few millimetres with use — a new lid that feels barely snug will be sloppy in three months. A new lid that feels firm everywhere without hot spots will settle into a perfect fit.
Head Shape Matters Too
Circumference tells you what number to look at on a chart. Shape tells you which brand to look at. Two riders with identical 58 cm heads can fit completely different lids — one round, one oval — because the helmet's internal shell shape doesn't match every skull equally.
If the helmet pinches at your forehead and temples but feels loose on the sides, you're a long oval in a round shell. If it crushes your cheeks before it touches your forehead, you're a round head in an oval shell. Neither is a fit problem you can pad out — it's a shape problem, and the only fix is a different brand.
Fit Check Once It's On
Even with the right measurement and shape, the only real test happens when you put the helmet on. Run through this in the shop, with the helmet on for at least five minutes:
- The cheek pads should press firmly against your cheeks. Smile — your face should resist
- No pressure points after five minutes. A hot spot at minute five is a migraine at hour two
- Skin on your forehead should move with the helmet when you push the chin bar up. If the helmet slides over your forehead, it's too big
- With the strap done up, you should not be able to roll the helmet forward off your head
- No gap between brow pad and forehead. None
Common Mistakes
Measuring over hair, hats, or ears. The tape goes against skin where it can, and skims hair flat where it can't. Going over a thick bun or a baseball cap adds an artificial centimetre — and that centimetre puts you in the wrong size.
Using a steel tape. Construction tapes don't bend cleanly around the curve of a skull, so they read short on one axis and long on another. Either get a fabric tape or use the string-and-ruler method.
Sizing up because "it'll break in." Helmet liner foam compresses around 15 to 20 percent over the first 15 to 20 hours of wear. That's enough to soften a tight new helmet into a perfect one — not enough to rescue a lid that was loose to start with.
Measure twice, shop once. A helmet you got the number right on is the difference between gear that works for you and gear you eventually stop wearing.
Once you have your number and your head shape, the catalogue narrows down quickly — and the buying-guide questions (lid type, safety standard, ventilation, visor system) become much easier to answer with confidence.
