The size chart
Helmet sizes use head circumference in centimeters. Every major brand, Smith, Giro, Sweet Protection, POC, Anon, Salomon, Atomic, Bern, works off the same scale. The letter sizes (S/M/L) cover the same ranges across roughly 90% of models.
| Size | Circumference (cm) | Circumference (in) |
|---|---|---|
| XS | 51-53 cm | 20.0-20.9 in |
| S | 54-55 cm | 21.3-21.7 in |
| M | 56-58 cm | 22.0-22.8 in |
| L | 59-60 cm | 23.2-23.6 in |
| XL | 61-63 cm | 24.0-24.8 in |
Ranges vary by brand. Smith and Giro group sizes into 4 bands (S 51-55, M 55-59, L 59-63, XL 63-67). POC, Anon, and Salomon often add an XS at 51-53. Always check the brand's own chart for the specific helmet you're buying, a Smith Medium and a POC Medium do not share an exact range.
If your measurement falls between two sizes, size down. The dial fit system at the back of every modern helmet has 1.5-2 cm of expansion, but it can't cinch a too-large helmet tight enough to stop rotation. A snug shell that loosens slightly is safer than a loose shell that tightens slightly.
How to measure your head
- Use a soft tape measure. If you don't have one, wrap a string and measure it against a ruler.
- Position the tape just above your eyebrows in front. About a finger-width above the brow bone.
- Run it around to the back, across the widest part of your skull. There's usually a small bony bump at the back, go just above that.
- The tape should be level all the way around. Not angled up or down.
- Snug, but not pulled tight. The tape compressing your hair flat is too tight.
- Read in centimeters. Round to the nearest whole cm.
Measure twice. If the two numbers disagree by more than half a cm, you're holding the tape at different heights, try again.
The fit test
The chart gets you within a size, but two helmets the same size from different brands can fit very differently. The shell shape matters as much as the circumference. Round-headed shoppers and oval-headed shoppers do not buy the same helmet, even at the same cm.
Once a helmet is on your head, run the fit test before buying:
- Sits level. The front edge should rest one to two finger-widths above your eyebrows. Not tilted back showing your forehead, not pulled down covering your brow.
- No pressure points. A snug, even feel all the way around. Specific spots that hurt now will hurt much more after two hours of skiing.
- Side-to-side test. With the chinstrap loose, grab the helmet by the brim and try to rotate it left and right. Your skin should move with it. If the helmet slides over your skin, it's too loose.
- Front-to-back test. Same hold. Rock it forward and back. Same rule, skin moves with the shell, not under it.
- Shake test. With the strap still loose, shake your head side to side and nod. The helmet should not move independently of your head. Any flop means a size down.
- Strap fit. Buckled, you should fit two fingers between strap and chin. Not one (too tight, you'll feel it on a long day). Not three (too loose, helmet can come off in a crash).
The single most common helmet sizing mistake is buying one that fits with a beanie underneath. Don't. Helmets are designed to be worn directly on your head; modern liners are warm enough on their own, and a beanie compresses unevenly under impact. Get a thin skullcap if your ears get cold.
Adjustable systems and what they actually do
Every modern ski helmet has a dial at the back. Spin it, the inner band cinches; spin it the other way, it loosens. The dial gives you 1.5 to 2 cm of micro-adjustment within a size.
What the dial cannot do: change the shell shape. If you're between an oval and a round head, the dial won't fix it, you need a different model. Brands that lean round: Smith, Salomon. Brands that lean oval: Sweet Protection, POC. Bern and Giro are usually closer to neutral.
Some helmets (Smith Vantage, Sweet Protection Switcher, Giro Range MIPS) add a second adjustment for height, the brim can move up or down half a cm. Useful if you wear a larger frame goggle and need to fine-tune the gap. Most helmets don't bother and most skiers don't miss it.
MIPS, WaveCel, and the rotation problem
Standard ski helmets are tested for direct, linear impact. Real crashes are almost never purely linear, most involve a glancing blow that rotates the head. Rotational force is the mechanism behind most concussions.
Three systems address this:
- MIPS (yellow dot inside the helmet). A low-friction inner liner that lets the shell slide 10-15mm relative to your head during a rotational impact. The most common system; in the lab data it reduces rotational acceleration by 10-30% depending on impact angle. Found in helmets from Smith, Giro, POC, Anon, and most others. Adds $30-60 to the price.
- WaveCel (Bontrager / Trek). A collapsible cellular structure that flexes laterally on impact. Manufacturer claims better rotational protection than MIPS; independent testing is mixed. Less common in ski than cycling.
- SPIN (POC, since deprecated in favor of MIPS in their newer line). Silicone pads inside the liner that allow shell-to-head movement. Phased out by 2021 but still found on older models on outlet pages.
Buying advice: if the helmet you want comes in a MIPS version, get the MIPS version. The non-MIPS versions of the same helmet test worse on rotational impact. Whether the non-MIPS version is "good enough" depends on how confidently you can predict the geometry of your next crash, which is a harder question than it sounds.
Goggle compatibility, the gaper gap
Ski helmets and ski goggles are designed to meet at a single line across the brow. When they don't, when there's a strip of forehead visible between goggle and helmet, that's the "gaper gap." Cosmetically dated, but more importantly: a cold spot, a wind tunnel into the helmet, and a sign the goggle frame doesn't match the helmet brim.
Most brands match their own goggles to their own helmets. A Smith goggle pairs with a Smith helmet without thinking about it. Mixing, Smith helmet, Oakley goggle, usually works but check the brim curve before buying. The goggle frame should follow the helmet brim line, not sit half a cm below it.
Helmets with adjustable brim height (Smith Vantage, Sweet Protection Switcher) handle mismatched goggle pairings best. Fixed-brim helmets are pickier.
Kids' helmets
Different rules for growing heads. The temptation is to buy a helmet a size up and let the kid grow into it. Don't. A loose helmet on a child is a helmet that rotates on impact, which is the failure mode you bought a helmet to prevent.
Buy on circumference now, not in twelve months. If the kid is between sizes, take the smaller one and use the dial to expand. Most kids' helmets cover roughly 49 to 56 cm in two or three sizes (XS / S / M, or "youth" / "junior").
Replace at the first season the dial maxes out, usually one season for a fast-growing kid, two for a slower-growing one. Used kids' helmets have unknown drop history; buy new.
FAQ
How long does a ski helmet last?
Three to five seasons of regular use, or one impact. Whichever comes first. The EPS foam liner that absorbs impact is one-use; once compressed, it doesn't recover. After a meaningful crash, even one that left the shell looking fine, replace it. UV exposure also degrades the foam; even a helmet that's only seen the inside of a closet is past its useful life by year seven.
Can I wear my old bike helmet skiing?
No. Different impact profiles, different temperature ranges, different ear coverage. Bike helmets are vented for hot weather and built for the impact angles cyclists hit at; ski helmets are insulated, cover the ears, and built for cold-weather brittleness in the foam. Use the right tool.
Is MIPS worth the extra money?
For most skiers, yes. Thirty to sixty dollars for measurably better rotational protection on the most likely concussion mechanism is one of the better safety upgrades in skiing. If you can only afford the non-MIPS version, the non-MIPS version is still a helmet and still works; it's not "MIPS or no protection."
Do I need a different helmet for backcountry skiing?
Most resort helmets are fine for non-technical backcountry. If you're skinning long distances, a lighter helmet with more venting (POC Tectal, Smith Summit) is worth the upgrade. Avalanche-specific helmets are rare and not necessary unless you're regularly skiing terrain where you might be hit by ice or rock.
Should I buy a helmet used?
No. The drop history of a used helmet is unknown, and a single impact you can't see compromises the foam liner permanently. New only. The cheapest new MIPS helmets (Smith Holt, Anon Helo) start at $60-80, less than most weekend ski lessons.
Does the size change with a beanie?
Don't size for a beanie. Modern helmet liners are warm enough for resort skiing in temperatures down to about -15°C / 5°F. If your ears get cold, get a thin under-helmet skullcap (4-6mm) rather than a beanie. A beanie compresses unevenly under impact and changes the geometry of the shell-to-head interface.
What's a "round" head versus an "oval" head?
If the front-to-back length of your head is roughly the same as the side-to-side width, you have a round head. If front-to-back is noticeably longer, you have an oval head. Most people are oval. Round-headed skiers tend to find Smith and Salomon helmets more comfortable; oval-headed skiers tend to prefer Sweet Protection, POC, and Giro.