The right bike helmet size – crucial for safety

bike helmet size

Cyclists are among the most vulnerable road users and are frequently affected by head injuries. This makes it all the more important to protect your head when cycling – but you absolutely need the right bike helmet size for effective protection. Here you can find out how to measure your bike helmet size. Also, which helmet size need for your kids, and when does your bike helmet fit properly.

bike helmet size

Although a bike helmet is not mandatory in the United States. It should be part of the basic equipment for children and adults when riding a bicycle. After all, the helmet helps to reduce the risk of injury and reduces the risk of long-term consequences from head injuries. To ensure this protection, the bicycle helmet must be the correct size. Only then does it sit firmly and securely on the head.

We also tell you what types of bike helmets are, how often you should replace your helmet, what costs to expect, and what to look out for when buying.

Important facts to choose the right bike helmet size

Especially occasional cyclists quickly get the idea of borrowing a helmet for the bike ride because the own purchase is supposedly not worth it. From the safety aspect, however, this is not recommended.

  • The helmet should fit well, i.e. it should also be comfortable to wear and not cause any pressure points.
  • The helmet size is always determined by the circumference of the head, which you only need to measure with a tape measure.
  • Choose a larger model if your head circumference is between two sizes. In addition to safety, wearing comfort is also important.
  • Of course, children should also wear a helmet. There are bicycle helmets for children in stores that are specially designed for small heads.
  • A helmet that is too large sits loosely and does not absorb the impact in the event of a fall, as well as a well-fitting helmet.
  • On the other hand, a small helmet will not protect all parts of the head as it should, increasing the risk of injury.

How to measure head for helmet?

Every head is different, and its circumference is only conditionally dependent on age or body size, which is why you should determine your individual bike helmet size. As a rule, there are the following helmet sizes: S (55/56 cm head circumference), M (57/58 cm), L (59/60 cm), and XL (61/62 cm), or double sizes such as M/L.

  • To properly measure the circumference of your head with a tape measure, wrap the tape measure around your head once from the center of your forehead above your ears.
  • At the back of the head, the tape measure should run across the widest part, not the back of the neck.
  • If you don’t have a tape measure at hand, a string or shoelace that you wrap around your head will suffice. You can easily read the determined length of a meter stick or a ruler.

Measure the size of the bike helmet correctly

However, these are not exact-fitting standard sizes – and therefore, you should measure your exact bike helmet size before buying. To do this, grab a measuring tape or thread, which you then measure with a ruler, and measure your head at the widest point about two centimeters above the eyebrows.

The tape measure should be above the ears at the bottom of the skull and not too deep in the neck. The measured head circumference is between two sizes? Then we recommend choosing the larger size – however, you must ensure that you can adjust the helmet. So that it holds without a chin strap even if you let your head hang down.

This video shows you exactly how to measure head for a helmet:

Bike helmet size: How the helmet fits properly

A bike helmet of the right size is comparatively comfortable and provides maximum safety in case of a fall. To do this, it should fit properly and not wobble or slip.

The bike helmet is adjusted with a chin strap and adjustment system so that the front edge of the helmet is at eyebrow level and position the helmet horizontally.

The fit is correct when the two straps form a triangle around the ear and are firmly tightened like the adjustment system. Of course, make sure that there are no pressure points and that the straps do not constrict the neck!

If you are a (sun) glasses user, be sure to wear your glasses when trying on the helmet. If neither the frame nor the lenses touch the helmet and nothing pinches, the bike helmet size is suitable for you.

Bike helmet size chart in centimeters

The size in centimeters of a bike helmet corresponds to the circumference of the head. Before buying a helmet, you should determine the circumference. If your measurement lies between two sizes, take the larger model if in doubt. After all, the helmet should fit snugly on the head but not pinch.

Although the numbers are not standard and the size chart of the manufacturers can differ, you can orient yourself to the following guidelines.

Head circumferenceBike helmet size
49-50 cmXXXS
53-54 cmXS
59-60 cmL
63-64 cmXXL

Bike helmet size for Kids

In young children, the head is relatively large in relation to the body – and they often fall head over heels. For this reason alone, children should always wear a helmet, whether in a bike trailer or child seat, on a running bike, or when riding a bike independently.

Bike helmet size for Kids

The size and fit of children’s bike helmets must also be right – a child’s helmet should never be bought “to grow into.” Only with the right bicycle helmet size is your child well protected in traffic. In addition, the children’s helmet should meet the safety standard.

To determine the correct helmet size for kids, the head circumference of the little ones is measured in the same way as for adults. The commercially available helmet size for children usually ranges between 44 and 60 centimeters.

For children, the head circumference is determined the same way as for adults. This is of course, smaller than for an adult, so there are special bicycle helmets for children. As a rule of thumb – but of course, cannot replace the individual measurement – applies:

  • 0-3 years: 44-49 cm head circumference – size XS
  • 2-7 years: 46-51 cm head circumference – size S
  • 3-9 years: 49-53 cm head circumference – size S/M
  • from 4 years: 52-58 cm head circumference – size M

Since children’s heads are still growing, it is essential to replace the helmet after a comparatively short time. Because here, too, the helmet must fit – buying a helmet that the child is still growing into is definitely not recommended. You can also read keep an eye on your bike with a GPS Tracker.

S, M or L? Calculating the right Bike helmet size.

Bicycle helmets are available in XS, S, M, L, or XL. In most cases, helmet sizes are also given in centimeters, which correspond to the circumference of the head. If you don’t find a unit of measurement on the helmet itself, check with the manufacturer. These usually provide size tables with a conversion.

However, caution is advised here: The tables of the individual manufacturers differ. A size L at Uvex does not necessarily have to be a size L at another manufacturer like Abus.

It’s best to try on different helmets in a specialty store anyway. This way, you can also find out directly whether the helmet is comfortable and offers adjustment options that guarantee that the helmet holds even without a chin strap when you bend your head down.

Bike helmet size: which models for which bike?

It is not only the bicycle helmet size that is relevant to safety. Riding style and bike are also important when choosing the fitting helmet:

Helmets for everyday use and touring

You need a rather simple helmet for the ride to work or a leisurely weekend tour. Aerodynamics, for example, does not play a major role here. However, it makes sense to pay attention to good ventilation. After all, only those who do not sweat under their helmet will wear it consistently.

Many standard and touring helmets now come with extras such as integrated lights or even smart helmets with intelligent functions. Also suitable for everyday use and touring is the airbag helmet.

Here, the head and neck area are protected when the airbag is triggered. The “helmet” is put on like a collar so that the head remains free. See the article “The Airbag Helmet” for more detailed information. Another alternative is folding helmets, which you can reduce in size by folding and thus easily transported in a backpack or bag.

Read the Folding article helmets – the head protection for the bag to find out which models and suppliers are available.

Helmets for road cyclists

Road bike helmets are designed especially to protect the face and front of the head. They are lightweight, well ventilated, and aerodynamically optimized.

Helmets for mountain bikers

Mountain bike helmets additionally protect the back of the head and temples. A full-face helmet is advisable for downhill riders, as this has an additional chin guard.

Helmets for BMX riders

Again, protection of the face, chin, and mouth is important. BMX helmets tend to be minimalist and have little ventilation.

Helmets for triathletes

The priority of the triathlon helmet is aerodynamics. Accordingly, it has a futuristic-looking tail tip that dissipates the airstream.

What you should look for when buying bike helmet?

Besides bike helmet size, there are many other criteria when choosing an optimal bike helmet. We would like to mention some of them here:

Wearing comfort

Of course, your future helmet needs to be comfortable, so it doesn’t snag on your handlebars. Breathable padding, integrated insect nets, and vents make a helmet much more comfortable.


Design can also play a role: Fancy helmets are often perceived as less uncool and are preferred. With helmets in eye-catching colors, cyclists are potentially seen better.


A prominent quality feature is the method of manufacture. Avoid bonded helmets if possible and instead, choose products that are made using the in-mold process and are much more robust.

How often the helmet needs to change?

We advise replacing your bike helmet every five years or even immediately in the event of a fall. Even if your helmet looks as good as new: UV radiation alone leads to material fatigue in the long term.

Cracks and holes in the upper material and internal or external dents are alarm signals that make replacement necessary. Of course, it is advisable to measure the bicycle helmet size again before changing it, as the head shape can change over time.

Bike helmet costs & benefits of bike helmet

Bicycle helmets come in all types and price ranges. Even though high-priced helmets usually get good reviews, quality doesn’t always have to be expensive. However, you should expect to pay at least $50 for a “normal” helmet. After all, it should offer real protection.

In any case, it is advisable to contact a specialist for advice, who will certainly be happy to assist you with regard to bicycle helmet size and model.

More tips for buying & bike helmet size

  • Road bike, mountain bike or BMX riders use special helmets that have, for example, extra ventilation, special aerodynamics or extra chin protection. Think about what you want to use the helmet for.
  • Even some everyday helmets now have helpful features such as an integrated light or an airbag that provides additional protection for the neck and head in the event of a fall.
  • When buying, look for testing and CE marking or GS seal.
  • Helmets that are not glued together but manufactured using a mold-in process are particularly robust.

We advise replacing the helmet after about five years, as the material can show signs of fatigue, which significantly reduces the protective effect.

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