Bike‌ ‌Helmet‌ ‌Size:‌ ‌How‌ ‌Should‌ ‌A‌ ‌Bike‌ ‌Helmet‌ ‌Fit‌ ‌


While riding a bike can bring a sense of accomplishment and independence to anyone, it can be dangerous if the rider fails to observe safety precautions. An unexpected fall from your road bike can easily cause serious brain injury. The good news, however, is that a properly-fitting helmet can reduce the risk. 

If you are purchasing a helmet for the first time, you may not understand how to determine the ideal bike helmet size. In this article, we will help you figure out the answer to how should a bike helmet fit?

How to Get the Right Bike Helmet Size

When purchasing a bike helmet, you must ensure that it is both comfortable and a good fit. In addition to compromising protection, an ill-fitting helmet can also compromise your will to wear it. 

 To find a good bike helmet size, you will need to follow the steps below: 

1. Measure Your Head’s Circumference 

Place a tape measure slightly above your ear and bring it across your mid forehead completely circling your head approximately 1” above the eyebrows. Take a couple of measurements to ensure you have the largest circumference. If you do not own a tape measure, you can use a string to measure the circumference and then measure this against a yardstick or ruler. 

Once you determine your circumference, you can use the following helmet sizing parameters to figure out which helmet to wear when biking:

  • Extra-small – Below 51 cm (20 inches)
  • Small – 51 cm to 55 cm (20 inches to 21.75 inches) 
  • Medium – 55 cm to 59 cm (21.75 inches to 23.25 inches) 
  • Large – 59 cm to 63 cm (23.25 inches to 24.75 inches) 
  • Extra-large – Above 63 cm (24.75 inches) 
  • One size fits all – This comes with an adjustable fit system 

2. Try the Helmet on 

When asking “how should a bike helmet fit?”, most riders do not realize the importance of trying the helmet on before paying for it. You should wear your helmet level on the head  – if the helmet is a good fit, it should not move freely when you roll your head from one side to the other. 

If the helmet is rolling around, this means that it is too big and will feel uncomfortable when you are riding your touring bike. If the movement is minimal, some extra padding may help provide a snugger fit. 

3. Adjust the Helmet for Proper Fit 

Before you can go on a bike touring trip, you will need to adjust the helmet to ensure you will have zero problems on the road. Proper adjustment at the beginning will help you avoid stopping your commuter bike now and then just to reduce helmet discomfort. 

First, you will need to adjust the tightness. The majority of the helmets will have an adjustment wheel at the back – you open this fully to put the helmet on and then twist it closed to get a snug fit before getting started with mountain biking. Keep in mind that fitness systems may vary from brand to brand – some helmets may adjust the fitness by making use of interchangeable interior foam pads. 

Next, buckle and tighten your chin strap. A common mistake that most people make when learning how should a bike helmet fit is not tightening the chin strap the right way. When tightened correctly, the straps form a comfortable V while resting under each ear. If the straps fail to form the V shape, adjust your buckle until they do. 

Finally, open your mouth wide to test the helmet. The bike helmet is supposed to press against your head’s top as you open your mouth. If this does not happen, tighten the chin strap a little and repeat. 

Bike Helmet Fit Tips 

4. Brand Sizing Varies

The sample bike helmet size numbers we showed earlier may differ slightly from brand to brand. Hence, always double-check the circumference of your head on the size you are thinking of getting. 

Also, similar to bike shoes, brands may use varying proprietary shapes for their helmet molds. For this reason, it is always a good idea to consider the helmet shape and compare it with your head’s shape – even better, try the helmet before paying for it. 

5. Go with the Smaller One if You Are Between Sizes 

For example, if your head size lies between medium and large, go with a medium bike helmet. An ideal alternative would be wearing a beanie or a cycling cap to improve a bigger helmet’s fit. 

6. A Good Fitting Helmet Shouldn’t be Annoyingly Tight 

The answer to the question “how should a bike helmet fit?” is that it should be snug. The helmet should sit level on the user’s head with the front edge at most 1 inch from the eyebrows so that the forehead is protected. If the helmet happens to move around noticeably when you push it back to front and side to side, all you will have to do is adjust the fit. 

Helmet Protection Choices 

The helmet’s primary function is to protect your head from injuries that result from the impact force of falling off your bike. The part of the helmet that protects you on your bike trip consists of an inner liner and an outer shell that has been integrated: 

  • Helmet Plastic Shell – This offers puncture resistance and allows your helmet to slide to impact, protecting your neck and head. 
  • Helmet Liner – This is made of high-grade Styrofoam (or expanded polystyrene foam). It protects the head by dissipating impact forces and slowing the head down. 

Even if the resulting damage is less obvious, rotational forces can lead to brain injury. To avoid brain damage, helmet manufacturers developed various technologies – all featuring varying names – to reduce the rotational forces resulting from a crash. For frequent riders or those who want added peace of mind, parting with some additional money for the following technologies may be a good idea: 

  • Multi-Directional Impact Protection System (MIPS) – This features a low-friction layer that redirects the rotational effects by allowing its impact-absorbing foam liner to slightly rotate during impact. 
  • WaveCel – Featuring a honeycombed liner material, this technology creates s a sophisticated “crumple zone” that absorbs both the rotational energy from an impact and the primary impact forces. 
  • Shearing Pads Inside (SPIN) – This technology features silicone-injected pads in a structure that moves inside the helmet’s shell to redirect rotational forces resulting from an impact. 

Bike Helmet Features 

The main features you will find on a bike helmet include: 

  • Ventilation – Vents on a helmet enhance wind flow over the rider’s head, keeping the rider cooler when pedaling and adjusting the bike gears. The more vents a helmet has, the lighter it is. 
  • Visor – The visor promotes sun-shielding – you will find visors on most mountain bike helmets.
  • Full Face Protection – Some mountain bike helmets feature a wraparound chin bar that offers face protection for racing or downhill mountain biking. 
  • Mount Compatibility – Some helmets are designed to allow you to snap a mount that holds a light or an action camera



Q: How Do I Know My Bike Helmet Size?


To figure out your ideal helmet size, you will need to measure your head’s circumference using a tape measure. Place the tape measure slightly above your ear and circle it around your head approximately 1” above the eyebrows. Once you determine your head’s circumference, use it to select a helmet using the helmet sizing chart.

Q: Do Bike Helmets Come in Different Sizes?


Bike helmets come in sizes ranging from extra-small to extra-large. Extra-small helmets have a size of below 20 inches, small helmets have a size of 20 to 21.75 inches, medium helmets measure between 21.75 inches and 23.25 inches, large measure 23.25 inches to 24.75 inches while extra-large measure 24.75+ inches.

Q: How Do I Know If My Bike Helmet Is Too Small?


The best bike helmet should have a snug fit. Hence, if your bike helmet is annoyingly tight, there is a high chance that it is too small for you.

Q: How Tight Should A Helmet Fit?


A properly-fitting bike helmet should be a little bit tough to slide on but feel comfortably snug once you put it on. When you move your head from side to side and front to back, the helmet should not shift too much.

Globo Surf Overview 

A helmet will only offer you the necessary protection if it fits you well. If you are wondering how should a bike helmet fit, you should know that it should be tight enough not to move around when you are riding your budget road bike but comfortably snug. If the helmet is too tight, it can make the whole ride uncomfortable.

Globo Surf
My name is David Hamburg. I am an avid water sports fan who enjoys paddle boarding, surfing, scuba diving, and kite surfing. Anything with a board or chance I can get in the water I love! I am such a big fan I decided to start this website to review all my favorite products and some others. Hope you enjoy!