How to Measure Helmet Size

Buying a helmet online without measuring your head is a coin flip, and the odds are worse than you think because no two brands size a helmet the same way. The good news is that measuring takes about five minutes and a soft tape measure. Do it once, do it carefully, and write the number down — it's the single most useful piece of information you can bring to any helmet purchase.

What you are measuring is the circumference of your head at its largest point. That is it. The number gives you a starting size against a manufacturer's chart, and from there it's about head shape and a proper fit check. Let's get the measurement right first.

What you need

A soft, flexible tape measure — the kind used for sewing — is ideal. If you don't have one, a piece of string and a rigid ruler works just as well: wrap the string, mark where it meets, then lay it flat against the ruler. A helper makes it easier to keep the tape level around the back, but you can manage alone in front of a mirror.

How to measure your head, step by step

1. Wrap the tape around the widest part of your head. That is roughly one inch (about 2.5 cm) above your eyebrowsat the front and around the widest bump at the back of your skull. This is the largest circumference — the number the helmet has to clear.
2. Keep the tape level all the way around, parallel to the floor. A tape that rides up at the back reads small and will send you to a helmet that's too tight. Check it in a mirror.
3. Pull the tape snug but not tight— firm against your skull, not digging in. You want the measurement your head actually is, not a squeezed version of it.
4. Read the number where the tape meets, in both centimeters and inches if you can. Charts use both, and having each saves a conversion later.
5. Measure three or four times, resetting the tape each time, and take the largest consistent reading. Heads are lumpy and it's easy to be a centimeter off on a single try; repeating it catches the mistake.

If you're using string, mark the overlap with your finger or a pen, then measure that length against the ruler. Same rules apply — widest point, level, snug, repeated.

Match your number to the chart — for each brand

Here is the part people skip: helmet sizes are not standardized.A 58 cm head might be a medium in one brand and a large in another, and the centimeter ranges behind the letters genuinely differ. So don't trust the letter — find the specific brand's size chart, look up your measured circumference, and read off theirsize. Do it again for every brand you're considering. It's a two-minute check that prevents the most common online-buying mistake.

As a rough orientation only — not a substitute for the brand's own chart — here is the generic range most makers land near:

Again: use this only to know roughly where you'll land. The brand's own chart is the one that counts, and the cutoffs shift from maker to maker.

One more wrinkle worth knowing: the letter size and the shell sizeare not the same thing. Better helmets are built on several physical shells, so a small head gets a genuinely small outer shell rather than a large shell packed with thick foam. That's why two helmets can both say "medium" and feel completely different on your head, and it's another reason to trust the specific model's chart and a real fit check over the letter alone. When you're comparing helmets, more shell sizes usually means a more precise fit across the size range.

Common measuring mistakes

Almost every "this helmet runs small" complaint traces back to one of a handful of measuring errors. Knowing them ahead of time is the easiest way to get the number right the first time.

• Measuring too high or too low. The widest part of your head is about an inch above the eyebrows, not up on the crown and not down at the hairline. Too high reads small and sends you to a tight helmet.
• A tape that isn't level. If the tape angles up toward the back of your head, the circumference reads short. Watch it in a mirror or have a helper keep it parallel to the floor all the way around.
• Pulling too tight. Cinching the tape into your scalp gives you a number smaller than your actual head. Snug and firm is right; strangling is not.
• Big hair.A lot of hair or a high ponytail can add a false centimeter or two. Flatten it, and if you always ride with a bun, at least know that the helmet won't account for it.
• Measuring once. A single reading is easy to get wrong. Three or four tries and the largest consistent number is the one to trust.

Measuring well for an online order

When you can't try a helmet on in a shop, your measurement is doing all the work, so it pays to be fussy about it. Take your number, then pull up the exact chart for the exact model you want — not a generic one, because a brand can even size two of its own helmets slightly differently. Buy from a retailer with a friendly returns policy the first time you try a new brand, because you may need to swap a size or discover the shell shape doesn't suit you. And when the helmet lands, don't ride in it or cut the tags until it clears the checks in how a helmet should fit. A measurement gets you the right size on paper; those checks confirm it on your head.

It's also worth re-measuring every few years, or whenever you buy your next helmet. Weight changes, and honestly just doing the measurement more carefully than you did as a nervous first-time buyer, can move you a size. Don't assume the size that fit your last helmet is still your size — measure again.

What to do if you're between sizes

Measure a 58.5 and the chart splits M and L right there? Size down.A new helmet should feel firm — snug enough that it's almost too tight the first few rides — because the cheek pads and crown padding compress as they break in, and a helmet that feels perfect in the shop will feel loose in a month. The smaller of two sizes breaks in to correct; the larger breaks in to sloppy.

The one exception is pain, not pressure. Firm and snug is right. A genuine pressure point that makes your forehead or temples ache is a shape problem, and sizing around it won't fix it — that's a sign to read our head-shape guide and try a different brand. To tell firm-and-fine from too-tight, run the helmet through how a helmet should fitonce it's on.

With your number in hand and your shape figured out, you're ready to shop properly. Our best motorcycle helmetsranking notes the fit character of each pick so you can match it to what you've just measured.