A helmet's protection depends on how accurately it fits your head. A loose helmet shifts on the head in an impact and loses the contact the inner foam needs in order to absorb energy; a tight one gives you a headache within half an hour and you start finding excuses not to wear it. In this guide we explain, step by step, how to measure your head circumference, how to convert centimetres into a size, why head shape matters at least as much as size, and how to try on a helmet in a shop. For helmet type, certification and budget, see the helmet selection guide; here we focus only on size and fit.
\n\nIf you have no tape measure, you can use a piece of string or a charging cable and then measure it with a ruler, but this method introduces a margin of error of a few millimetres. Because size boundaries are 1–2 cm apart, this difference can push you into the next size up or down.
\n\nIf you enter your measurement in the helmet and glove size tool, you will immediately see which size you fall into and whether you are on a borderline.
\n\nThe table below is the general range used by most European and Japanese brands. Between brands there can be a shift of up to 1 cm; always check that brand's own chart before buying.
\n| Head circumference | Size |
|---|---|
| 51–52 cm | XXS |
| 53–54 cm | XS |
| 55–56 cm | S |
| 57–58 cm | M |
| 59–60 cm | L |
| 61–62 cm | XL |
| 63–64 cm | XXL |
| 65–66 cm | 3XL |
What if you are on the borderline? For example, if you measured 58.5 cm, try both M and L. The general tendency is to choose the tighter-feeling option for a new helmet, because the inner padding settles a few millimetres in the first few weeks. But if the tightness reaches the level of \"painful pressure\", the smaller size is the wrong choice.
\n\nTwo people can both have a 57 cm head circumference, but one has a round head and the other a long oval one. Looking at the helmet from above, the ratio between the head's front-to-back length and its side-to-side width determines whether the shell shape will suit you.
\nTo work out your head shape, ask someone to photograph you from directly above, or wet your hair and look at it from above in a mirror. Some manufacturers state on product pages which model suits which head form; the real criterion is feeling the helmet you try wrap evenly everywhere.
\n\nIn quality helmets, two, three or even four different outer shell sizes are made for different size ranges. In cheap helmets there is usually one or two shells, and the size difference is provided only by the thickness of the inner padding. In that case an XS helmet means a large shell for your head: it looks heavier and catches more wind. If you are very small or very large, give priority to models with more than one shell size.
\nSome brands sell the cheek pads separately. If the helmet fits your head overall but feels loose or tight at the cheeks, it may be possible to change the cheek pads. Pad replacement generally does not fix pressure at the crown and forehead; in that case the shape is not right for you.
\n\nThe measurement gives you a starting size; the decision is made after trying on. Follow this order:
\nPrices online can be attractive, but buying a helmet without trying it on is risky. If possible, try the same model in a shop, and order once you are sure of your size. Read the return and exchange conditions on the order; many sellers do not take back a helmet that has been tried on, has had its tag torn off or its visor film removed. When trying the helmet at home, do not remove the protective films; just wear it in a clean environment for 20–30 minutes.
\nTo see price ranges, you can look at the pages for full-face helmet recommendations and prices, modular helmets if you prefer a flip-up chin bar for the city, and open-face (jet) helmets for the open type.
\n\nEven after you have found the right size, keeping the fit is up to you. Remove and wash the inner padding regularly in the way the manufacturer recommends; padding that has hardened with sweat and lost its shape reduces how well the helmet holds onto your head. If the cheek pads become noticeably thinner within a few years and the helmet starts to wobble, on models with spare pads it may be enough to renew just the pads. Do not hang the helmet on the motorcycle's mirror or the end of the handlebar; the inner foam can be crushed at these hard points. If there has been a big change in your weight or hairstyle (for example you have had long hair cut short), check the fit again. If you carry a passenger, the passenger's helmet must pass the same tests; on the back seat the head is more exposed to the wind and to the risk of hitting the rider's helmet. Do not use an adult helmet for child passengers; choose a child's helmet suited to the head measurement. Finally, if you have dropped the helmet, assume the inner foam has taken an impact even if you see no mark on the outer shell, and have it checked by an expert; crushed foam will not absorb energy in the next impact.
\nWhen you find a helmet that suits your head, note down its model and size. Even when moving to a new version of the same model the shell can change, so try it on anyway, but the note quickly narrows your options.
\n\nFor the right helmet size, first measure your head circumference three times, find your starting size from the chart, then choose the shell that suits your head shape by trying it for at least 15 minutes. A helmet that is snug but not painful, does not rotate and does not tip forward is your helmet. You can enter your hand circumference in the same tool for your glove size too: the glove size guide is the next step.
\n\nIn the general chart, S corresponds to a head circumference of 55–56 cm, M 57–58 cm, L 59–60 cm, XL 61–62 cm. There can be a difference of up to 1 cm between brands, so check the brand's own chart.
\nTry both for at least 15 minutes. If it is not painful, generally choose the tighter one; the inner padding settles a few millimetres with use and the helmet loosens a little.
\nThe inner padding generally settles within the first 15–20 hours of use. The tightness eases during this time, but a clear pressure point does not go away; in that case the shape does not suit your head.
\nIf the helmet turns independently of your skin with the strap fastened, it is too big. Try one size down; if that does not fit either, look for a different shell shape or a model with the option of thicker cheek pads.
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