Kart helmet sizing is model by model rather than brand by brand. Sparco alone run six different ladders across their kart range, and none of them matches their car helmet ladder. The good news is that every size on this site carries the head measurement inside the size name, so you can ignore the letter completely.
Read the number, not the letterOur size options are written like “M (57cm-58cm)”. Measure your head once and pick the option whose centimetre range contains your number. That is all you need to do, and it works across every brand and model on the site.
Measure the head
1One inch above the eyebrowsThen round the widest part at the back. Soft tape, level all the way round.
2Take the largest readingMeasure three or four times and use the biggest number you get.
3Hair as you driveMeasure with the hair down or tied as it will be under the helmet.
4Children grow, helmets do notBuy to the measurement today. A helmet bought big to last two seasons moves on the head, and you will be replacing it anyway when it is outgrown.
The homologation decides how big the helmet goes
This is the thing that catches parents out. Snell-FIA CMR is the junior standard and every CMR helmet we stock stops at around 59 cm, because it is designed for a child. If your driver measures more than that, a CMR helmet does not exist in their size and you need a CMS, a Snell K or an FIA 8878 helmet instead. Check which your series accepts before you shop.
ECE 22-06 helmets are road motorcycle homologated. They are popular for practice, arrive-and-drive and indoor karting, and they cover the widest size range, but most competition series will not accept them. Check your regulations first.
Ladders by brand
All measurements are head circumference in centimetres.
BellNumeric on most kart models. Pick your measured size.▼
StiloLettered, and the ST6 KRT offers two different L liners.▼
Stilo state their helmets run slightly smaller than other brands, so if you are on a boundary go up. The ST6 KRT lists an L at 58 cm and an L at 59 cm; those are two liner thicknesses in the same shell.
SparcoSix different ladders. Read the centimetres in the size name.▼
None of these matches Sparco’s car helmet ladder, and several do not match each other. A Sparco kart M can be 56-57, 57-58 or 58-59 cm depending on which model you are looking at.
OMP and AraiBoth use the same ladders as their car helmets.▼
How it should fit
Snug enough that it is slightly awkward to pull on, with the cheek pads pressing the cheeks up. With the strap done up you should not be able to rotate the helmet forwards off the head. The lining beds in over the first few sessions, so a helmet that feels merely comfortable in the box will be loose by the end of the season.
For a child, check it again at the start of every season rather than assuming last year’s helmet still fits. Heads grow faster than you expect and the fit goes off before the helmet looks any different.
Tell us the series as well as the measurementHead circumference in centimetres and which championship or club you are running in. The homologation narrows the choice more than the size does, and we would rather get both right at once. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
Ladders read from the size options on our own products, which carry the head measurement in the size name. Bell numeric models follow Bell’s published HP, Carbon and Pro chart. Arai and OMP kart ladders match their published car ladders. All checked 2 August 2026.
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