Bike Helmet Size Chart: How Should a Bike Helmet Fit?

To make sure that a helmet fits you snuggly and properly, you need to go through the bike helmet size chart. Through the help of bike size data of different brands available, we have made this guide to help you make the right decision.

It includes a step-by-step guide on size charts from multiple brands, including Giro, Bontrager, Bell, Nutcase, etc. So, let’s dive right into the main discussion without any further ado:

Detailed Bike Helmet Size Chart For Beginners

Standard Sizing Parameters

The standard size parameters for bike helmets according to multiple brands go as under:

  • Extra small: below 20” or (51cm)
  • Small: (51cm–55cm) 20″–21.75″
  • Medium: (55cm–59cm) 21.75″–23.25″
  • Large: (59cm–63cm) 23.25″–24.75″
  • Extra-large: (63cm) above 24.75″

One size fits all: has a highly adjustable fit system.

Based on these parameters, we take a look at the bike sizing chart of multiple brands as under:

Giro Helmet Size Chart

Being one of the most popular and most reputable helmet brands in 2022, Giro offers models that could fit your head with due comfort and convenience.

While purchasing a Giro helmet, keep these size chart metrics in mind:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

That’s the standard sizing of Giro helmets. However, the brand does offer some exceptions.

For instance, the size increases for full-face bike helmets as they may run narrow due to their internal padding and other accessories.

Similarly, Giro also offers universal sizing that includes the circumference ranging from 50 to 57 cm for women, 54-1cm for unisex helmets, and 58-65 cm for extra-large heads.

Nutcase Helmet Size Chart

Nutcase helmets are also quite popular in the United States. The major reason for its popularity is that these helmets are durable, they feature a unique design, and most Nutcase models have MIPS technology integrated with them.

Here is a complete size chart for those riders who want to get themselves a Nutcase helmet:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Not to mention, Nutcase offers helmets for small babies as well. Their sizes in centimeters might range from 48 to 52, and in inches, the size converts from 18 to 20.5 inches.

Bern Limited – Helmet Size Chart

Bern also specializes in making helmets that could keep your heads protected, especially when involved in a crash.

The good thing about the brand is that you’ll find multiple sizes ranging from extra small to extra-extra-large and check whether they go side by side with your head’s circumference or not.

The table goes as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Scott Bike Helmet Size Chart

Scott is a well-renowned brand for producing full-face, open-face, and daily commute biking helmets.

The size chart for Scott helmets is as follows:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Lazer Sport – Helmet Size Chart

Lazer is a global brand specializing in cycling helmets that ensure complete head and skull area protection.

The sizing chart that this manufacturer offers is as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Thousand – Helmet Size Chart

Specializing mostly in traditional helmets, Thousand offers full-face models that can keep your breathability intact while protecting your head from impacts and damages.

The bike size chart for this brand goes as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Bontrager Road Helmet Size Chart

Another brand is famous for producing mountain bike helmets, both open and full-faced.

The manufacturer allows you to choose from a variety of helmets based on the circumference of your head.

Bontrager offers the following sizes:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Bell Helmet Size Chart

Bell is a pioneer of making comfortable and snug helmets that would ensure protection against rotational forces as well as sudden impacts.

The size range for this brand goes as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

TeamObsidian Helmet Size Chart

Not as famous as the likes of Bontrager or Bell, TeamObsidian helmets are surely making their place in the market.

The complete size chart that this helmet manufacturer offers are as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Smith Adult Helmet Size Chart

Smith produces helmets with MIPS integrated with them to ensure that your head and brain remain conscious in case you go through a serious fall.

The helmet size chart for the adult category goes as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Smith Junior Helmet Size Chart

Like the adult category, Smith has also focused on manufacturing helmets for teenagers and toddlers.

The sizing category for youth is as follows:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

Garneau Bike Helmet Size Chart

Garneau produces helmets for women, men, youth, and children simultaneously. The models have usually got a unique shape, durable body, and can protect a rider from harsh incidents at the same time.

The sizing chart for Garneau is as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

iOutdoor Bike Helmet Size Chart

Last but not least, iOutdoor is also famous for producing some of the best MTB helmets with a snug and comfortable fit.

We take a look at the sizes it offers as under:

Head SizeSize in CentimetersSize in Inches
XL63-6524-25
XS45-4917-19
S51-5520-21
L59-6323-24
M55-5920-23
XXLN/AN/A

How to Measure Head for Bike Helmet?

You’ll need to get started with taking multiple measurements of your head, followed by finding the right size of the helmet from different manufacturers.

But, the whole process will certainly become easier in this guide. Let us get started with how to measure the head circumference to get to the right size first:

Determining Your Head Size:

Measuring the head size means you’ll get to measure the circumference of your head and then match it with the available sizes present in the market.

You’ll need a tape measure or a charging cable, or simply a string to get started with the whole process.  We’ll also recommend keeping a ruler by your side if you use a charging cable or a string.

The whole process of how to size a bike helmet goes as under:

Step 1: Measure the Circumference of Your Head:

Wrap the measuring tape around your head in a way that it’s one inch above your eyebrows and take the first measurement of the circumference of your head.

Note it down and take two more head measurements to find the average size accordingly. In case if you don’t have a measuring tape available, use either a charging cable or simply a string to measure the circumference of your head.

You can measure it later with the help of a ruler. We’ll still recommend that you use a measuring tape for correct measurements. 

Step 2: Try the Helmet Yourself

Go to a local bike shop and start wearing helmets according to the circumference measurement of your head. Make sure that you wear the helmet in level to your head. Besides, the helmet should not move when you move your head abruptly.

If it moves, you are wearing a helmet that’s way too large for your head. Keep trying the helmets, and you’ll finally find the one that will fit snuggly.

Step 3: Determining a Proper Fit

The last thing to check after you wear the helmet is to see whether it fits properly or not. In that aspect, the helmet should sit right above your eyebrows. As far as the backside is concerned, it should not touch the nape of your neck.

Adjust the chin straps in a way that there’s a distance of only two fingers in between.  Check the helmet again by moving your head here and there, and if it does not move, you have found a perfectly sized helmet for your head.

People Also Ask:

How do I know my bike helmet size?

Start with measuring the circumference of your head with a measuring tape. After that, find the closest option available and put it on. It should fit snuggly and not slide after you adjust the chinstrap. If you feel that the helmet is too narrow or wide, go for another sizing option.

What size helmet is 53cm?

53cm or 20 inches fall into the small size category. Bikers with a small head circumference usually go for such helmets as they offer a comfortable and snug fit without any hassle.

What size helmet is 57cm?

The 57cm marks fall into the medium category, and bike helmets with this type of sizing are a bit wide compared to the small size. They could also ensure a snug fit for the riders with medium head size.

Final Takeaways:

The bike helmet size chart from multiple brands does not offer a 100% guarantee that the exact helmet will fit you.

That’s one of the reasons we, as well as all helmet manufacturers, recommend visiting a local shop first to try a helmet practically and determine the size accordingly.

Once it’s sorted out, you can keep ordering the same size for the rest of your life unless you are not a kid.

Good Luck!!

From riding to school since the age of 13, attending BMX races and events with his dad to himself conquering 10+ trails across the globe. For Rob, his Giant Stance 29 2 2020 is the friend that makes everything better. He is also a proud member of the International Mountain Bicycling Association (IMBA).

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