What Does 65cm Mean in Helmet Sizing? (Size, Shape and Fit)

What the 65 cm measures

Helmet sizes are based on one measurement: the circumference of your head at its widest point. That line runs across your forehead about 2.5 cm (one inch) above your eyebrows, just above your ears, and around the fullest part of the back of your head. A helmet labelled for 65 cm is designed for a head that measures 65 cm along that line.

The number doesn't describe the helmet's outside size. A helmet for a 65 cm head is much bigger than 65 cm around on the outside, because of the shell and the protective foam liner. That's also why big-head helmets look bulky: the protective layer has to be the same thickness whatever your head size.

How 65 cm maps to letter sizes

Every brand sets its own ranges, so treat this as a rough guide and always check the brand's chart in centimetres.

The motorcycle row is where people run into trouble. One brand's XXL may be 63 to 64 cm and another's 64 to 65 cm. If you're 65 cm and you buy "XXL" without checking, you might get a helmet that's a centimetre too small, which is enough to cause a headache inside half an hour. Our helmet size chart shows typical ranges by type.

How to measure your head properly

You need a soft tape measure. A metal tape or a ruler won't work around a curve.

1. Position the tape across your forehead about 2.5 cm above your eyebrows, just above the tops of your ears, and around the widest part of the back of your head.
2. Keep it level and snug. Not loose, not squeezing.
3. Look in a mirror to check the tape hasn't slipped down at the back or ridden up at the front.
4. Measure three times and use the largest number.
5. Write it down in centimetres. Helmet brands' cm ranges are more reliable than their inch conversions.

If you're between two sizes, for example 64.5 cm with ranges of 63 to 64 and 65 to 66, try both if you can. If you can't, the larger size with thicker cheek pads is usually the better bet than squeezing into the smaller one. Our guide on how to measure your head for a helmet has photos of each step.

Head shape: why 65 cm isn't the whole story

Two people with a 65 cm head can need different helmets, because heads aren't all the same shape. Looking down on someone's head from above, the outline is usually described as one of three shapes:

If you have a long oval head and wear an intermediate oval helmet, it'll press on your forehead and the back of your head while leaving gaps at the sides. You might be tempted to go up a size, but then the helmet moves around. The real fix is a helmet built for your shape. Many motorcycle brands state which shape each model is designed for; it's worth looking for that before you look at the letter size.

To check your shape, ask someone to look straight down at your head from above, or take a photo from above with your hair flattened. If the width side to side is clearly narrower than the length front to back, you're probably a long oval.

Shell sizes and big heads

Most helmet makers use a small number of outer shell sizes and vary the thickness of the foam liner to cover a range of head sizes. A medium shell might cover XS to M with different liners, and a large shell might cover L to XXL.

For a 65 cm head, this matters in two ways:

• You want a model where your size has its own shell, or is at the lower end of a shell's range. If 65 cm is the very biggest size squeezed into a shell, the liner may be thinner than ideal and the helmet may not sit right.
• Big-shell helmets are heavier. A 3XL helmet can weigh noticeably more than the same model in a medium. That's normal, but it's worth trying the weight before a long ride.

How a helmet should fit

Once it's on and the strap is done up, run through these checks. They apply to motorcycle and bike helmets alike.

1. Snug all round. Firm, even pressure around your head and on your cheeks (for full-face helmets). No gaps you can slide fingers into easily.
2. No pressure points. Wear it for 10 to 15 minutes indoors. If you get a sore spot on your forehead or the back of your head, it's the wrong shape or too small.
3. It moves your skin. Hold the chin bar or the sides and try to turn the helmet. Your skin and cheeks should move with it, rather than the helmet sliding over them.
4. Roll-off test. With the strap fastened, push up at the back of the helmet, then pull up at the front. It shouldn't roll forward off your head or back to expose your forehead.
5. Eye line. On a bike helmet, the front edge should sit about two finger-widths above your eyebrows. On a full-face helmet, you should have a clear view without the brow of the helmet cutting into your top line of sight.

Cheek pads and comfort liners in motorcycle helmets compress as you wear them in, so a new helmet should feel quite snug at first. It shouldn't feel painful. If it hurts in the shop, it'll hurt on the road.

Safety standards to look for

A helmet that fits but isn't certified isn't doing its job. Check for the right certification for the activity, which is usually printed on a label inside the helmet or on the back.

Sizing doesn't change these standards, but some cheaper helmets aren't certified in their very largest sizes. Check that the size you're buying is covered.

When to replace a helmet

Replace any helmet after a crash or a significant impact, even if it looks fine. The foam liner is designed to crush once to absorb energy, and the damage is often invisible. The Snell Memorial Foundation recommends replacing helmets about every five years even without a crash, because liners and materials degrade over time. Check the manufacturer's guidance for your helmet too.

Hat size and 65 cm

If you're used to buying fitted caps or traditional hats, 65 cm is about a size 8⅛. You can work out a hat size by dividing the head circumference in inches by about 3.14. That's useful for comparison, but don't use a hat size to buy a helmet. Hats stretch and helmets don't. Our hat size chart and the explainer on what a 58 band means in hats cover hat sizing.

Buying a helmet online with a 65 cm head

• Filter by centimetre range, not letter size.
• Check which shell size covers your size if the brand lists it.
• Look for the head shape the model is made for.
• Check the return policy before ordering. Many shops accept returns on unworn helmets if you only try them indoors with the tags on.
• Read reviews from people with large heads. They'll tell you which "XXL" really fits a 65 cm head.

If you ride motorcycles, the rest of your kit needs to fit too. Our guides to measuring for motorcycle gear and the motorcycle jacket size chart cover jackets, trousers and gloves.

If you sell helmets online

Shoppers with large heads have usually been burned before, so they look hard at the size chart. Help them:

• List every size with its centimetre range, not just letters.
• Say which head shape each model is designed for.
• Show which sizes share a shell.
• Say clearly if the largest sizes carry the same certification as the rest.

Our explainer on pinchmark versus bar-lug helmet sizing covers another sizing system shoppers sometimes run into.

Frequently asked questions

Sources and standards

1. FMVSS 218, Motorcycle helmets (US Department of Transportation)The US federal standard for motorcycle helmets, shown on helmets as DOT certification.
2. UN ECE Regulation No. 22 (22.06)The motorcycle helmet standard used across Europe and many other countries.
3. CPSC 16 CFR Part 1203, Safety standard for bicycle helmetsThe mandatory US standard for bicycle helmets.
4. Snell Memorial FoundationVoluntary helmet standards; recommends replacing helmets about every five years.
5. Tailor Size Guide helmet size chartOur reference for typical size ranges by helmet type, used across the helmet pages on this site.