Short answer: measure your head circumference about 2.5cm above your eyebrows and above your ears, at the widest point, then check that number against the specific brand's chart. Helmet sizes are not standardised. A 54cm head is a Small in Giro, Kask, Shimano, HJC and Oakley, but a Medium in Merida, KED and Safety Labs.
Contents
- How to measure correctly
- The same head, different sizes
- Size charts by brand
- If you fall between two sizes
- Measurement is not fit
- Heat, sweat and helmet life in India
- Frequently asked questions
How to measure correctly
Use a soft tape measure, or a length of string measured against a ruler afterwards.
- Wrap the tape around your head roughly 2.5cm above your eyebrows and just above your ears.
- Keep the tape level front to back. Tilting it is the most common source of error and can easily cost you a centimetre.
- Find the widest point, which is usually slightly above the bump at the back of the skull.
- Pull it snug but not tight, and measure to the nearest half centimetre.
- Measure twice. If the two readings differ, take the larger one.
Measure with your hair as you normally wear it for riding. A tied-up style and a loose one can differ enough to change the size.
The same head, different sizes
This is the part that catches people out. Brands set their own ranges, so the size on the box tells you nothing on its own.
| Brand | 54cm head | 56cm head | 58cm head | 60cm head |
|---|---|---|---|---|
| Giro (Super Fit) | S | M | M | L |
| Kask | S | M | M | L |
| Shimano | S | M | M or L | L |
| HJC | S | M | L | L |
| Oakley (ARO3, ARO5) | S | M | L | L |
| Merida | M | M | M or L | L |
| KED | M | M | M or L | L |
| Safety Labs | M | M | L | L |
At 56cm almost everyone agrees. It is at the ends of the range that brands diverge, which is exactly where a wrong guess leaves you with a helmet that does not fit. Never order by the size you wore in a different brand.
Size charts by brand
Giro
| Range | S | M | L | XL |
|---|---|---|---|---|
| Adult Super Fit | 51-55 | 55-59 | 59-63 | 63-65 |
| Super Fit full face | 51-53 | 51-55 | 55-59 | 59-63 |
Giro also uses Universal sizing on some models: Women's Adult 50-57, Unisex 54-61, Extra Large 58-65. Check which system the specific model uses, because Super Fit Small and Universal Women's are not the same thing.
Abus
Abus varies by model more than any other brand we stock, so the model name matters as much as the size.
| Model | S | M | L | XL |
|---|---|---|---|---|
| Gamechanger | 51-55 | 52-58 | 59-62 | |
| Gamechanger TT | 51-55 | 52-58 | 58-61 | |
| Stormchaser | 51-55 | 54-58 | 59-61 | 61-63 |
| Aventor, Cliffhanger, MoDrop, Taipan, Xoxo | 51-55 | 54-58 | 57-61 | |
| MoTrip, Gamechanger 2.0, Powerdome, Airbreaker 2.0 | 51-55 | 54-58 | 57-61 | |
| Viantor, Macator, Aduro 2.1 | 51-55 | 52-58 | 58-62 | |
| Airbreaker | 51-55 | 52-58 | 59-61 | |
| Montrailer, Pedelec | 55-58 | 58-61 | ||
| Moventor | 52-57 | 57-61 |
Kask
| Size | Head circumference |
|---|---|
| S | 50-56cm |
| M | 52-58cm |
| L | 59-62cm |
Shimano
| Size | Head circumference |
|---|---|
| Small | 52-56cm |
| Small / Medium | 50-56cm |
| Medium | 55-59cm |
| Medium / Large | 55-61cm |
| Large | 58-61cm |
| X Large | 61-64cm |
| Unisize | 54-61cm |
Shimano is unusual in stating a preference: if you fall between two sizes, they advise the smaller one. Full face MTB models are excluded from this chart.
HJC, Merida, KED, Safety Labs and Oakley
| Brand | S | M | L |
|---|---|---|---|
| HJC | 51-56 | 55-59 | 58-61 |
| Merida | 54-58 | 58-62 | |
| KED | 52-58 | 58-61 | |
| Safety Labs | 48-54 | 54-57 | 57-61 |
| Oakley ARO3, ARO5 | 52-56 | 55-59 | 58-62 |
Safety Labs starting at 48cm is worth noting, because it is the smallest adult size among the brands here and suits riders other brands cannot fit.
For MET, Bell and Rudy Project, sizing varies by model and the charts sit on their own pages. Message us if you would rather we just tell you.
The full range sits in cycling helmets.
If you fall between two sizes
Brands overlap their ranges deliberately, so a 55cm head is legitimately both a Giro Small and a Giro Medium. There is no single correct answer, but there are useful rules.
- Going smaller gives a more secure fit and less movement, and is Shimano's stated recommendation. It is the better choice if you find helmets tend to rock on your head, or if you have fine hair.
- Going larger gives more airflow and room, which matters in Indian heat, and is the better choice if you have thick hair, wear a cap or a headband under the helmet, or find retention dials dig in.
- The retention dial is not a size adjuster. It fine tunes a shell that already roughly fits. If you are winding it fully closed or fully open to make a helmet work, you have the wrong size.
Measurement is not fit
Circumference gets you the right shell size. It does not tell you whether that shell suits your head shape. Heads vary between rounder and longer front to back, and helmet moulds do too. A correctly sized helmet on the wrong shape produces pressure points at the forehead or at the sides, and it will still be uncomfortable at hour three no matter how the dial is set.
Check these five things with the helmet on and the dial adjusted:
- Level, not tilted back. The front edge should sit roughly two finger widths above your eyebrows. A helmet tipped back leaves your forehead exposed.
- No rocking. With the straps undone, shake your head firmly side to side and nod. The helmet should move with your head, not slide on it.
- Skin moves with the helmet. Push the front of the helmet upward with one hand. Your eyebrows should lift. If the helmet slides without moving your skin, it is loose.
- Straps form a V under each ear, with the junction sitting just below the earlobe.
- Chin strap snug. You should be able to open your mouth wide and feel the helmet pull down slightly.
No pressure points anywhere. A hot spot you can feel in the shop becomes a headache on a long ride.
Heat, sweat and helmet life in India
Three things about helmet ownership here that the size chart cannot tell you.
- Sizing slightly larger has a real benefit in heat. Airflow through a helmet depends on space between the pads and your scalp. A helmet sized tight enough to sit hard against the head vents poorly, and on a 38 degree morning that is genuinely uncomfortable rather than merely a preference.
- Sweat degrades pads faster than riding does. Salt breaks down the foam and the adhesive. Remove the pads and hand wash them in mild soap every few weeks. Most helmets come with a spare set, and replacements are cheap. A helmet that has become loose over a year is often just compressed pads.
- UV shortens helmet life. Manufacturers commonly quote three to five years for the shell. Sustained sun exposure degrades EPS foam and the shell bonding, so at the Indian end of that range, three years is the sensible planning figure rather than five. Store the helmet indoors rather than hanging on the bike on a balcony.
When buying, check the helmet carries a recognised safety certification, usually CE EN1078 or CPSC, printed on a label inside the shell.
Frequently asked questions
Does a helmet need replacing after a crash even if it looks undamaged?
Yes, always. A helmet works by crushing, and the EPS foam compresses permanently to absorb impact energy. That compression frequently leaves no visible mark, because the outer shell springs back while the foam beneath does not. A helmet that has taken a significant impact has already spent its protection and will perform far worse next time. This applies to dropping it hard onto a concrete floor, not only to crashing.
How often should I replace a helmet that has never been crashed?
Every three to five years, and closer to three in Indian conditions. The EPS foam and the bonding between foam and shell degrade with ultraviolet exposure, heat cycling and absorbed sweat, none of which leaves visible evidence. Storing the helmet indoors rather than on a sunny balcony materially extends its life. Check the manufacturing date, usually moulded inside the shell, rather than counting from when you bought it.
Can I wash helmet pads, and how?
Yes, and you should every few weeks in this climate. Peel the pads out, they are usually held by hook and loop, and hand wash them in lukewarm water with a mild soap. Never use a washing machine, hot water, or solvent-based cleaners, all of which break down the foam and adhesive. Air dry them away from direct sunlight. Do not wash the shell itself with solvents either, since some degrade the polycarbonate.
Do MIPS helmets need a different size?
No, the size is based on the same head circumference and MIPS models use the brand's standard chart. The low friction liner sits inside the helmet and takes up a small amount of internal space, so a MIPS version can feel marginally snugger than the non-MIPS equivalent in the same size. If you are at the very top of a size range, that difference is worth checking in person before buying.
Is a more expensive helmet safer?
Not necessarily. Every helmet sold with a valid certification has passed the same impact tests, so a certified budget helmet meets the same minimum standard as a flagship one. What the extra money buys is lighter weight, better ventilation, more refined retention systems, and often rotational impact technology such as MIPS, which addresses a type of impact the basic standards do not test. The single largest safety factor remains fit, and a well fitting affordable helmet beats an expensive one that rocks.
Come and try it on
Measurement narrows the choice; head shape decides it. We keep helmets in stock at our Kondapur store so you can try the size your measurement suggests and the one either side of it. Send us your measurement on WhatsApp and we will tell you which models are likely to suit before you make the trip.
