Ultimate Bike Helmet Size, Fit, & Style Guide

large group of cyclists wearing bike helmets

Wearing a bike helmet is a no-brainer but only a fairly recent requirement. Bike helmet technology did not begin until the 70s, and helmets did not develop their hard shell and inner foam structure until the 90s. Now, we know that wearing a helmet is essential to any bike ride. Bike helmets can protect the brain from severe damage, but only as long as they fit your head properly. When you fall, a properly sized helmet takes a hit for you. It absorbs impact and distributes the rotational force on the head. If your bike helmet isn’t sized or fitted well, then it’s no longer effective. Measuring your bike helmet size and finding the right fit is a simple but vital step to a safe ride.

Why is fitting a bike helmet properly important?

A properly fitted bike helmet is essential to safety. All bike helmets made in the U.S. must pass safety standards set by the Consumer Product Safety Commission, and many bike helmets are designed with additional safety features that further reduce the risk of injury on impact. In most states, it’s illegal not to wear a bike helmet.

But if your helmet doesn’t fit well, then it becomes unreliable. The safety claims aren’t effective if your helmet shifts out of place on your head. Just like your bike shorts and cycling jerseys, finding a helmet that fits helps you perform well and feel comfortable. And when it comes to your safety, you must also make sure your helmet is fitted for full protection. Just having a helmet on isn’t always enough.

Bike helmet sizing

Bike helmets are generally sized small, medium, or large based on your head circumference in centimeters. The measurements associated with different sizes may vary across manufacturers. Measuring your head for a bike helmet is a great place to start, but don’t stop there. The best way to find out if your helmet really fits is to try it on. Every head shape is different and some bike helmets fit certain head shapes better than others. Once you’ve picked a bike helmet for your head, adjust the retention system, side straps, and chin strap for the most secure fit.

How to measure your head for a bike helmet

Measuring your head for a bike helmet is your first step in finding the best-fitting bike helmet. Grab a soft measuring tape and wrap it around the back of your head and across your forehead. Then note the measurement in centimeters. If you don’t have a measuring tape, wrap a piece of string around your head and mark where the string meets your starting point. After you’ve found your head circumference, compare the number to a bike helmet size chart to find your size.

example of how to measure your for a bike helmet

Bike helmet size chart

Below is an example of a bike helmet size chart. However, you should always check a helmet manufacturer’s size chart to make sure you get the right size since sizes may vary with different helmets. This chart includes the average size ranges for bike helmets.

HEAD CIRCUMFERENCE 51–55 cm 55–59 cm 59–63 cm

How should a bike helmet fit?

Once you’ve selected a bike helmet based on your head size, try it on to find the proper fit. Never settle on a helmet before trying it on because every head shape is unique, and you won’t know just by looking at it which model will work best for you. A helmet should sit level on your head, not tilted too far forward or backward. It should also sit low on your forehead. If your helmet is positioned correctly, you should be able to fit only one or two fingers between your helmet.

A bike helmet should be snug but not pinch. You can adjust the retention mechanism at the back of the helmet and the side straps and chin strap for a custom fit. To make sure your helmet is snug enough, try to yawn. When you open wide, the top of your helmet should press down on your head. Many bike helmets have an opening for a ponytail so you don’t have to stuff it in the helmet and compromise the helmet’s safety. And lastly, a properly fitting bike helmet should be comfortable. If your helmet is uncomfortable, you may not have one that fits well.

Types of bike helmets

There are three broad types of bike helmets–road, mountain, and commuter helmets. Within these different categories you can find different styles and features that make certain helmets stand out as best for your preferred riding style, whether racing, recreational, or fitness.

Road bike helmets

Road bike helmets are lightweight and well-ventilated. The lightest helmets are best for racing but also the most technologically advanced and expensive. Good road bike helmets have deep channeling that allows air to circulate through the helmet and back out in an efficient way, cooling you down but not slowing you down. Road bike helmets have no visors because they would obscure vision when crouched in a road cycling position.

Time trial helmets are similar to road bike helmets with an extra emphasis on aerodynamics. This means they have few ventilation channels to prevent wind drag and an elongated rear to propel wind past the helmet.

Mountain bike helmets

Mountain bike helmets are heavier than road bike helmets because they require extended protection. They have greater coverage to protect from branches–they peak in the front, they’re lower in the back, and some have full face coverage to protect the chin and mouth. The heavier weight is not a disadvantage because speed is not usually the focus when mountain biking.

Commuter bike helmets

Commuter bike helmets help keep riders safe in traffic collisions and covered in bad weather. They often have small visors to keep the sun rays and raindrops out of your eyes. When commuting on a bike comfort is second to safety rather than speed or aerodynamics, so commuter helmets may have some ventilation to keep you cool but not as deep channeling as road bike helmets.

What features to look for in a bike helmet

  • Polycarbonate shell and EPS foam: Start with the basics. For optimal protection, helmets should have an outer shell that cracks on impact and inner foam that minimizes the force of impact. Helmets manufactured in the U.S. will meet these criteria, but if you order a helmet from outside of the country, you need to make sure they meet fundamental safety criteria.
  • Adjustable straps and retention mechanism: Good helmets have both adjustable straps and a retention mechanism so you can attain the best fit for your head shape.
  • Additional safety features: All certified helmets are safe, but some helmets may have more advanced safety features than others. For instance, MIPS, Wavecel, or SPIN technologies minimize rotational forces of impact that shift your helmet and make you more vulnerable to a head injury. Learn more: What is Mips & How Does It Work?
  • Ventilation channels: If you’re a road cyclist, you need great ventilation with a helmet that moves airflow through in the most aerodynamic way.
  • ANGi sensor: Some helmets include this sensor that will signal your phone to call for help if you’ve fallen and can’t access it or are incapable of using your phone.
  • Lights: Front and rear lights are especially for commuter helmets in traffic, but they’re also a must-have for any type of cyclist who rides in the dark.
  • Turn signals: Turn signals are great for commuters on the road to help make your next move more obvious to cars around you.
  • Visor: For an MTB helmet, a visor is essential for protection from any hanging or falling branches, rocks, or other rubble.

Now that you know how to find the right size and fit for your next bike helmet, choose from our top 10 recommendations of the best road bike helmets to find one you love cycling in.

Finding the right size, fit, and style for any cycling gear enables you to perform your best and ride comfortably. Learn how to size and style your bike shorts or how to measure your sit bone width for your most suitable saddle size.

You might also like: