Helmet letters mean less here than anywhere else on the site. At 58 cm round the head you are a Bell M, a Sparco M and an Arai M, but a Stilo L and a Schuberth L. Measure once, then read your own number off the chart for the brand you are buying.
Measure your head
Bell put it best on their own guide, and every brand here measures the same way. Take the circumference about an inch above your eyebrows at the front, and at whatever point at the back gives you the biggest number. Take it three or four times and use the largest reading.
1Soft tape, level all the way roundA cloth tape, not a steel one. If the tape dips at the back you will read short.
2One inch above the eyebrowsThen around the widest part of the back of your head.
3Take it more than onceUse the biggest reading you get, not the average.
4Hair downMeasure as you would drive. A ponytail or a thick balaclava changes the answer.
Your size in every brand we stock
Find your measurement in the left column. A dash means that brand does not make a size at that measurement, not that it is out of stock.
Sparco column is the Stealth RF ladder, which is what almost everything we stock from them uses. OMP column is the GP-R. Bell HP/Pro covers their HP, Carbon and Pro models, which use a different chart from the rest of the Bell range.
What catches people out
Bell run two different charts
Bell publish one chart for most of the range and a second for the HP, Carbon and Pro models. They are not the same. On the general chart a 56 cm head is an XS; on the HP, Carbon and Pro chart the same head is an S. That is why some Bell helmets on the site are sold as S, M, L and others as 54cm, 55cm, 56cm and so on up to 61+. The numbered ones are the HP, Carbon and Pro models and you pick your measured size directly.
Stilo run small, and skip some sizes
Stilo say it themselves: their helmets “run traditionally a hair smaller than other sizes on the market”. On top of that the ST6 ladder steps unevenly, so 56, 60 and 62 cm have no size of their own. If you measure at one of those, or you are on a boundary anywhere in the Stilo range, go up rather than down and ring us first.
A shell size is not a helmet size
Every brand here builds a handful of outer shells and then changes the padding inside to make the sizes. Going up a size inside the same shell costs you nothing in bulk or weight. Crossing into the next shell up makes the helmet visibly bigger and noticeably heavier, which you feel over a long stint and which matters if you are tight for room in the car.
Shell splits published by Stilo and Schuberth. Arai build more outer shells than anyone else here and also offer different shell shapes for rounder and longer heads, which is worth knowing if other brands have never quite fitted you.
Full charts by brand
Bell, general rangeGT6, RS7, Mag, X-1, K1 and the rest. 51 to 68 cm.▼
Bell, HP / Carbon / ProHP6, HP7, HP10, HP77, GT6 Carbon, RS7 Carbon. Sold by measured size.▼
These are the models listed on the site as 54cm, 55cm and so on. 61+ is Bell’s largest liner in this range.
StiloST6 GT, GTN, FN and the Venti range. Runs slightly small.▼
The Venti Trophy Rally range uses a different, continuous ladder: XS 53-54, S 55-56, M 57-58, L 59-60, XL 61-62, XXL 63-64. If the uneven steps above put you between sizes, that range may cover you.
SparcoStealth RF, Stealth RF Carbon, Flux RJ-i and the RJ range.▼
Sparco also publish a generic six size chart (XS 53-54, S 55-56, M 57-58, L 59-60, XL 61-62, XXL 63-64). The seven size ladder above, with an ML at 59 cm, is the one the Stealth RF range actually uses, so go by that for the helmets we stock.
AraiGP-6S, GP-7, GP-Jet 3. The most shell sizes of any brand here.▼
SchuberthSF3, SF4 and SP1. Note the L+ size between L and XL.▼
Zamp and OMPSmaller ranges. Neither publishes a chart, so these are the sizes as we list them.▼
The OMP J-Rally uses a different ladder again: S 57-58, M 58-59, L 60-61, XL 61-62. Ring us for that one.
How a helmet should fit
Tight, then tighter than you think
A new helmet should be snug enough that it is slightly awkward to pull on, and the cheek pads should push your cheeks up. The lining compresses with use, so a helmet that is merely comfortable in the showroom will be loose by the end of the season. Do the roll-off test: with the strap done up, take the back of the helmet and try to rotate it forwards off your head. If it moves, it is too big.
Open face and full face are not the same fit
An open face sits differently because there is no chin bar pulling the shell forward, and several brands build their open face range on a separate set of shells. If you are moving from one to the other, do not assume your size carries across. Stilo in particular build the Venti open face on three shells and the ST full face on two.
Glasses
Say so when you order. Some models take a glasses channel in the cheek pads and some do not, and it is much easier to sort out before the helmet ships than to feed the arms in afterwards.
Buying a helmet and a head restraint together?The helmet needs FHR anchor posts fitted, and where a helmet is sold as a package here it already has them. If you are buying the two separately, tell us and we will make sure the posts and the tether length match the helmet you have chosen.
Send us your measurementGive us your head circumference in centimetres and the model you are looking at. Helmets are the one thing worth getting right first time, and we would far rather check it with you than process a return. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
Bell from bellracing.com. Stilo shell and fit information from stilohelmets.com. Sparco generic chart via Racecar Engineering, model ladder from the range we stock. Arai from whyarai.co.uk. Schuberth from their published SF4 and SP1 data. Zamp and OMP from the sizes on the products themselves. All checked 2 August 2026. If the chart in the box disagrees with this page, the box wins and we would like to know.
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