What it does
A helmet only protects if it fits. Measure around your head with a soft tape, type the number, and this tool gives the usual size for it, with fit checks and the safety marks to look for.
The size table is a common one, and makers differ by a size either way, so treat the answer as a starting point and try the helmet on. For the running cost of the bike see fuel cost, and engineering unit converter turns inches into centimetres.
How to use it
- Wrap a soft tape measure around the widest part of your head: about 2 cm above your eyebrows and over the widest point at the back.
- Pick cm or inches, type the number, and read the size.
- Try the helmet on and go through the fit checks.
What each setting does
- Unit: cm or inches. Inches are converted at 2.54 cm per inch.
- Size: the band your measurement falls in. Near the edge of a band you are told to also try the next size.
Worked example
57 cm gives M, and so does 22.5 in (which is 57.15 cm). 56.9 cm is S, but at the top of the band, so you are told to try M too.
FAQs
Which mark must the helmet have? India: the ISI mark (BIS IS 4151). USA: the DOT sticker (FMVSS 218). Europe and many other countries: the ECE 22.06 label. Look for the label inside, not just a sticker on the outside. Check the official source for what your own state or province accepts.
How tight should it be? Snug all over, with no pressure points. When you shake your head with the strap fastened, the helmet and your skin should move together.
Is an old or dropped helmet fine? Replace a helmet after a hard knock and generally after about five years, or as the maker advises.
Not safety or legal advice.
Where the numbers come from
- Size bands (XS 52-54.9, S 55-56.9, M 57-58.9, L 59-60.9, XL 61-62.9, XXL 63-64.9 cm): a common table; makers differ, so these are estimates. Always check the maker's own chart.
- India: BIS standard IS 4151 (ISI mark), Bureau of Indian Standards, bis.gov.in. USA: FMVSS 218 (DOT mark), NHTSA, nhtsa.gov. Europe and many other countries: UN Regulation 22 (ECE 22.06 label). Canada: provinces generally accept DOT or ECE labels; check your province. Checked 2026-11-10; check the official source.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.