How to Measure Bike Helmet Size: 3 Expert Tips

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Bike helmets are crucial for any cyclist, regardless of their experience, cycle route or bike style. So, making sure you know how to measure bike helmet size that is suited for you is key to making sure that you’re both safe and comfortable when you’re out on a ride.

Most fatal accidents – or even deaths – caused on bikes are due to head injuries, and this is largely due to riders not wearing helmets, so it’s paramount that you know how to find a suitable helmet, as well as how to fit it correctly.

The following article will act as a guide for just that, giving you the knowhow on bike helmets, so you know exactly how to find and fit yours, and make sure you’re always safe on the road!

How Do Bicycle Helmets Work?

Bike helmets work as most helmets do. They act as a sort of safety shell in order to protect your head from damage. Bike helmets are usually constructed from a form of polystyrene foam that’s then coated in a hardened plastic shell.

The reason for this construction is for two reasons – the foam is designed to absorb the force of any strong impacts, whilst the hardened shell acts as a good waterproofing and protective layer, to prevent the polystyrene from falling apart. All bike helmets must meet the European Safety Standards (CE EN 1078) in order for them to be considered safe.

Depending on the quality of your helmet, the plastic cover may actually be molded to the polystyrene to create one piece. As well as this, you may have foam or padded strips on the inside for added comfort when it’s placed on your head.

You may also have added features, like an adjustable headband, ventilation holes, or even added safety features to prevent against sharp object or impact rotation.

How to Measure Bike Helmet Size

bike helmet size

Here are a few tips you can follow:

1. Measure It

The first thing you’ll want to do when finding out your ideal helmet size is to measure your head. To do this, wrap a tape measure around your head just above your ears and eyes, until it’s gone all the way around.

Take note of the measurement that appears on the tape measure, and then measure again, at least 2 or 3 times in total. It’s always best to go with a slightly larger helmet than a slightly smaller, as it’s less likely to cause discomfort.

2. Put the Helmet On 

After measuring your head in order to determine the ideal helmet size, you should try a helmet on to see if it actually fits well.

The helmet should fit snugly and squarely on your head, without moving or shifting to the side. If it’s a tad too large, consider adding some padding inside just to make it fit better.

3. Make Sure It Fits Properly

To make sure the helmet fits properly, it should sit an inch or so above your eyebrows, but not so high that it goes above your forehead. Similarly, make sure it doesn’t touch your neck, but still covers most of the back of your neck.

As for the chin strap, this should fit tight enough that the helmet is unable to move and bounce, but you should still be able to fit two fingers between the strap and your chin at a squeeze – again, this may take some adjusting to get right.

How to Adjust Your Bike Helmet

Here are the steps you should follow when adjusting your bike helmet:

Adjust Tightness

After placing your bike helmet on and making sure it’s level and straight, you’ll then want to adjust the helmet’s tightness.

Many helmets nowadays have a plastic band inside that can be adjusted with a dial at the back. If yours had one included, adjust this until it feels snug on your head, but not so tight that it causes any pain or discomfort.

Buckle the Chin Strap

After adjusting how tight the helmet is, next, fasten the chin strap and tighten that too. Again, this should be a firm fit, but not so tight that it causes any irritation or discomfort.

Open Your Mouth As Much As You Can

As one final check, with the helmet tightened and the chin strap fastened, open your mouth as wide as you can. Whilst doing this, the chin strap should tug on your chin, and the helmet should push down against your head. If not, then the helmet is too loose, and you’ll need to make some adjustments.

Extra Trips on Bike Helmet Fit

Here you have a few extra tips we have prepared for you:

Size Varies from Brand to Brand

Like with bikes themselves, sizes between different brands or manufacturers can vary a lot. A ‘medium’ helmet size by one brand might be completely different to a ‘medium’ from another brand.

To avoid getting a helmet that doesn’t fit well, it’s important to double-check the circumference measurement of the helmet, rather than the helmet size itself.

Always Go with the Smaller Size

Sometimes it’s better to go with the smaller size rather than the larger size if you’re between sizes. This can account for things like haircuts, taking out the padding, or a few extra adjustments just to make it fit better. Some full-grown adults wear youth helmets with no problems at all.

Make Sure You Have a Comfortable Fit

As mentioned earlier, your helmet should be snug, tight and secure fit, without being so tight that it causes any irritation or discomfort. It should remain level on your head, and not move around when completely fastened and tightened. It’s better to be slightly too tight that slightly too loose.

Helmet Protection Options

It goes without saying that a helmet’s primary purpose is to protect you from impact or injury both on your bike or when falling off.

The outer shell acts as a protective barrier for the helmet itself, whilst the inner foam polystyrene acts as an absorbent to protect you.

  • The plastic shell protects against scrapes, bumps and scratches, and stops the inner polystyrene from breaking down.
  • The inner polystyrene foam absorbs impact and prevents your head from taking damage during a collision.

Rotational damage or torsion during impact is also known to cause damage to the skull, brain, neck and/or nervous system during incidents, so some high-end helmets have integrated technology to prevent this from happening.

If you ride regularly, or on a route with heavy traffic, it might be worth spending the extra cash for a helmet with this included. 


WaveCel technology uses a sort of honeycombed lining/material that’s designed to act as a ‘crumple zone’ within the helmet. This helps absorb a lot of the impact to again prevent you from taking damage during an accident.


MIPS (Multi-Directional Impact Protection System) technology is often integrated into high-end helmets. It uses a friction-resistant layer to displace any rotational effects of an impact, to prevent this from damaging your head.


SPIN (Shearing Pads Inside) technology makes us of silicone-injected pads within the helmet’s structure. These move inside the shell in order to displace rotational force on an impact, for an added element of protection.

Features of Bike Helmets

bike helmet between sizes

These are the main bike helmet features:


Helmet visors shield your eyes from sunlight and protect them from grit, dust, and dirt.


Ventilation holes in bike helmets work to increase the wind and airflow to your head, in order to keep you cool and comfortable during a ride.

Mount Compatibility

Some helmets allow you to mount torches or cameras on them, for added visibility, or to film a ride for your safety or entertainment.

Full Face Protection

Certain mountain bike helmets offer full face protection, which protects your face and chin from impacts as well as your head.

When Should You Replace Your Helmet?

It’s not always easy to know when a bike helmet needs replacing. Certain bike helmets are only designed to absorb one single impact – as part of their inner lining is designed to break during this impact to absorb most of the force.

So, if you’ve encountered any type of impact, it’s a good idea to replace your helmet. If you haven’t been in an accident, consider replacing your helmet after around five years, as your helmet is likely to have worn down after this time.

How to Deep Clean Your Helmet?

Cleaning your helmet correctly isn’t just a way of ensuring personal hygiene, but it stops both your head, and the helmet itself, from stinking over time.

Oil and grease from your hair and skin can sink into the helmet, and after a while, it’ll start to develop an odor. To clean it, use a cleaning solution that’s suitable for contact with skin, and wipe over with a cloth. Consider some kind of safe air freshener too, just to freshen it up.

Final Thoughts

Bike helmets are a key element in making sure you stay safe, secure and comfortable on a bike. When measuring and fitting a bike helmet, the key things to remember are that your helmet should be snug but not too tight, that the chin strap keeps it securely in place, and that the helmet itself is of sound construction, just to ensure that it does offer the desired protection if you do happen to get involved in an accident.

David Miller

My name is David and I have been an outdoor guy for as long as I can remember. I have a strong passion for the great outdoors in general and specifically camping. I am the kind of person who spends more time outdoors than indoors. I am a staunch believer in the fact that outdoor life should be well lived because it's in the natural, serene, and untamed wild that we find out who we truly are. Let’s take the journey together.

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