How to measure for a bike helmet

How to measure for a bike helmet

A good fitting bike helmet is crucial for a biker’s safety. Have you ever had to replace your bike helmet? Or are you getting your child a bike helmet for his new bike? How do you determine the perfect fit? How can you improve a bike helmet’s fit to suit your head size? In this article, we will answer these queries as we understand how to measure a bike helmet. Let’s get started!

The Right Fit

As a rule of thumb, the right-fitting bike helmet should have a close yet not so tight but stable fitting around the head. You should be able to face upside down or endure moderate impact with the headgear staying comfortably intact around the head. The head mask must lean on the head in a straight position (not inclined backward).

It should also be an inch or less from the eyebrows. This position ensures protection for your forehead.  In addition, this right fit determines how to measure a bike helmet accurately.

Before you grab a measuring kit, consider the helmet’s construction. The shape of the headgear will vary from one manufacturer to the other. There isn’t also a mandatory sizing standard that manufacturers use to label their helmets as small, medium, or large. Hence, a medium-sized headgear from one brand may have a small or large fitting and be categorized differently by another brand.

Check the design of the shell and the liner. Also, consider how seamlessly the helmet’s impact protection system rotates from side to side. The right fit of the bike helmet will affect how the ventilation, visor, hair port, straps, and other additional features function.

How to Measure For a Bike Helmet

How to Measure For a Bike Helmet: Detailed Steps

Helmet Sizing

Use a tape measure or a marked string to determine the circumference around the most extensive section of the head. Ideally, this is usually a few centimeters above the eyebrows. Compare the parameters you get against the manufacturer’s helmet sizing.

Alternatively, use such sites as and to match the head circumference parameters against the helmet size chart. These charts offer a guide on the most appropriate helmet size based on the head circumference.

Are You in Between Helmet Sizes?

Sometimes, the head size may not match any of the helmet sizes on the manufacturer’s chart or any other helmet-sizing source. In this case, you should go for a smaller scale. Alternatively, use various helmet accessories to get a perfect fit from a large helmet.

You could also use a cycling cap, a balaclava, a universal fit ring, or sizing pads under your vented helmet to fit the large size evenly.  

For a child, you have to remove or reduce these accessories when the child’s head grows.


Helmet Shape

Once you determine the right helmet size, consider the various brands available. Choose a brand whose helmet shape closely matches your head shape.  

Italian helmet brands, for example, tend to be narrower. The US-made helmets, on the other hand, have a rounded shape.

what size helmet if between sizes

Try It On

Once you settle for the helmet brand that best fits your head

 shape, try it on.  Use the sizing wheel and the chin straps to fit the helmet perfectly.

You should be able to barely open your mouth unrestrictedly after buckling the chain straps into a V-shape just below the ears. Confirm this by placing a finger in between the straps and the chin. The thumb should pass through in a firm fit.

Also, try turning the helmet from side to side. The straps should not move more than an inch on either side. If the straps do run a lot, tighten them even further.

If possible, use a mirror to check for the right leveling of the headgear. A helmet with proper leveling is low lying, and the front covers the forehead properly.


Overall, your comfort and safety will dictate how to measure for a bike helmet that fits your needs. In as much as the higher priced helmets tend to have a wider size variety to choose from, you should never compromise these two aspects for a stylish helmet. Bikers should be willing to spend some time trying out several headgears before settling on one.

6 thoughts on “How to measure for a bike helmet”

  1. Riding a bike, or cycling can be very exciting, especially while trying to learn. This is also an important activity to work on physical fitness. It’s always ideal to take the basic safety measures to prevent harm during accidents.

    Hence, there is need to have the right safety gadgets, like a helmet on while cycling. However, it’s not enough to own a helmet, it should also be of the right size. This is to ensure, you receive adequate cushion in case of a crash.

    The thumbs rule is easy to follow and can be used to check that, you have the right size of helmet. Dies the thumb rule apply also to children? Seeing that they grow quickly.

    Expecting to hear from you soon, thanks for sharing.

    • Hi, Louis and thank you.

      When you are in active sports like cycling, for example, it is an absolute must to use all basic safety. For example, we should do all we can to defend the brain, but on the way, we can have fun at the same time.

      Using a helmet is a smooth and troubleless method to do that.

      From New York comes statistic that nearly all bicyclists who died (97%) were not wearing a helmet.

      For a child, you have to remove or reduce these accessories when the child’s head grows.

      If I can help you with anything else, or if you have any questions, don´t hesitate to contact me.

  2. Well written. So far I’ve bought exactly the way you wrote. I agree with you that it is necessary to measure well and repeatedly to try the helmets. It is true that, in adults, there is no such problem as in children.For adults, buy it once and you can have it for quite some time. It’s a little harder for children, … different sizes and the head grows every year. I did not know the thumb rule, very day you learn something new :). Thanks again for a good article.

    • Hi, Andrej and thank you.

      Thank you for your kind words. Great to hear about your benefit of the article.

      It is essential to have in mind that adults need too to change the helmets regularly. It recommended that they do it each three years as an idea. Why? Because the foam degrades of weather, sweat and other factors from the environment. And if the helmet gets a knock, for example, things fall on it, you should check it out too.

      If I can help you with anything else, or if you have any questions, don´t hesitate to contact me.

  3. Wow.. This information is so timely and helpful.

    I have been contemplating of changing my bike helmet for the past few weeks. So lucky to have stumbled on your post. I love the way you outlined the review. With this I now know what and what to check for before selecting a particular kind of helmet for myself.. Thanks for this.

    • Hi, Michael and thank you.

      Thank you for your kind words.

      Changing or buying a bike helmet is essential to have high on the priority list because it is such an important safety thing.

      Good luck.

      If I can help you with anything else, or if you have any questions, don´t hesitate to contact me.


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