The fitting guide Helmet sizing made simple
Helmet Size Chart: How to Measure and Find Your Fit
A tape measure gets you a starting size. A good helmet fit takes one more step: checking your head shape, the specific manufacturer's chart, and how the helmet actually feels when you wear it.
Measure in centimeters, find that measurement on the brand and model's size chart, then check for an evenly snug fit with no painful spots or independent helmet movement. Do not pick a size by “medium” or “large” alone.
01 / Start here
How to Measure Your Head for a Helmet
A flexible tailor's tape is easiest. You can also wrap a non-stretch string around your head, mark the overlap, and measure the string with a ruler. Ask someone to help you keep it level if possible.
Find the right line
Place the tape just above your eyebrows, over your ears, and around the fullest part at the back of your head. Keep it level rather than sloping toward your neck.
Wrap it snugly
Pull the tape comfortably against your hair without squeezing. Avoid a thick hat, ponytail, or anything that changes the measurement.
Record and repeat
Write down the circumference in centimeters. Repeat two or three times; if results differ, recheck your tape placement before shopping.
The measurement path and fit check follow the NHTSA motorcycle helmet fitting guide and LS2's official measuring instructions.
02 / Size reference
Motorcycle Helmet Size Chart (Manufacturer Example)
Helmet size labels are not universal. The chart below shows the published head-circumference reference from SMK Helmets so you can see how letters relate to measurements in one real manufacturer's lineup. Those numbers are SMK's values, not a fit guarantee for HJC, LS2, Bell, Shoei, or any other brand.
These are the specific SMK size labels and circumference figures, with inches rounded to one decimal (1 in = 2.54 cm). They are chart reference points, not universal size ranges. SMK also lists youth and XXS sizes; consult the original chart for those.
Important
Between two sizes?
There is no dependable one-size-fits-all rule to always round up or down. First consult the manufacturer of the helmet you're buying, then try both adjacent sizes if possible. Shape, liner and cheek-pad fit can change the answer.
Go directly to a brand's own chart
A chart is only the first filter: helmet designs vary even within the same brand. Check the chart attached to the particular model or product page whenever one is supplied.
03 / Beyond the number
Your Head Shape Matters as Much as Your Size
Two riders can both measure 58 cm and still need different helmets. One may have a rounder head and another a longer front-to-back shape. Manufacturers vary their interior profiles, which is why a correct circumference alone doesn't prove a good fit.
Long oval
Noticeably longer front to back than side to side.
Intermediate oval
A middle-ground oval profile common in many street helmets.
Round oval
More similar in front-to-back and side-to-side proportions.
To estimate yours, have a friend look from above while your hair lies flat. Don't judge from your face shape in a mirror. According to the NHTSA, forehead hot spots can mean the helmet is too round for your head, while side pressure can mean it is too elongated. A different helmet shape is often a better fix than simply changing the size.
04 / The real deciding step
Five Checks for a Proper Helmet Fit
Put on the candidate helmet and fasten its chin strap according to the manufacturer's instructions. The goal is firm, even contact — not pain, loose gaps or a helmet that rotates independently of your head.
Even pressure
Feel consistent contact around the crown. The helmet should be snug without a sharp point pressing into your forehead or temples.
Cheeks supported
On a full-face helmet, cheek pads should contact your cheeks firmly. They should not leave large gaps or force your jaw into a painful position.
Minimal movement
Shake your head gently and move the helmet side to side. It should move with your skin, not wobble on its own or slide across your eyes.
Strap secure
Buckle and adjust the chin strap as designed. Check that the helmet cannot readily roll off your head. Revisit the manufacturer's instructions for its retention system.
Wear it for a while
Keep the helmet on indoors for roughly 30–45 minutes before riding. Some pressure points appear slowly. Persistent pain is a reason to reassess the model or fit.
Fit-test guidance: NHTSA and RevZilla's motorcycle-helmet fitting guide.
05 / Solve the usual problems
What Different Fit Problems Usually Mean
The helmet rocks or slides
Recheck the chart and try the next appropriate size or another model. If a full-face helmet spins freely while your head stays put, the fit is not secure.
One sharp spot on your forehead
A change in internal profile may help more than a larger size. Compare rounder and longer-oval models without accepting an otherwise loose fit.
Headache or painful temples
Take it off. A snug helmet should not cause lasting pain. Try a different size or interior shape; don't modify its protective liner.
One size feels loose; the next hurts
Try another model or brand. Manufacturer-approved alternate cheek pads or liners may help when the brand explicitly offers them.
Safety rating and fit are separate checks
For motor scooters and mopeds used on U.S. roads, look for a properly labeled, FMVSS No. 218–compliant motorcycle helmet and a correct fit. NHTSA explains that the DOT label is a manufacturer self-certification, not a government product endorsement. A bicycle-only helmet is not automatically a substitute for a street-motorcycle helmet. Check the rules where you ride.
Read NHTSA's helmet selection and DOT-label guidance ↗Keep reading
After You've Found Your Size
Need a local shop or accessories supplier? Browse TheScooterist's U.S. scooter and repair directory and call ahead to confirm whether a business stocks helmets and offers fitting help.
Quick answers
Helmet Sizing FAQs
How do I know what helmet size I am?
Measure the widest circumference of your head with a soft tape placed just above your eyebrows. Compare the result in centimeters with the exact manufacturer's chart, then confirm fit by trying the helmet on and checking for even pressure and minimal movement.
Is a 57 cm head always a medium helmet?
No. SMK's published guide lists medium at 57 cm, but other brands and individual models can use different boundaries and interior profiles. Treat 57 cm as your measurement, not a universal letter size.
Should I size up or down between helmet sizes?
Don't automatically do either. Consult the helmet maker's instructions, try both nearby sizes if available, and consider another model if one is loose while the other creates painful pressure. A secure fit matters more than the letter on the label.
How tight should a new motorcycle helmet feel?
It should feel firmly snug and evenly supportive, particularly around the crown and cheeks on a full-face design. It should not slip when you gently shake your head or create painful forehead and temple pressure. Recheck it after 30–45 minutes indoors.
Can I wear a bicycle helmet on a moped?
Don't assume a bicycle helmet meets motorcycle helmet requirements. For road-going motor scooters or mopeds in the United States, check the applicable vehicle and local requirements and choose a properly labeled compliant motorcycle helmet. A correctly sized helmet is necessary whichever category you ride.