The primary reason for buying a motorcycle helmet is safety and protection to your head in the event of an accident. To get the best protection your helmet needs to provide a really good comfortable fit. A bad fitting helmet can come off in an accident even if the chin strap is done up.
In order to find a motorcycle helmet with the correct fit, you should know your head size measurement before you buy any helmet. Here's the golden rule for finding a good comfortable fit:
Your head size + Your head shape = comfortable fit
First you need a small metal tape measure or a cloth tape to take your measurement. If possible ask someone to help you do the measuring in order to get a more accurate measurement.
|
Size |
Centimeter |
Inches |
Hat Size |
|
S |
55-56 |
21 1/2 - 22 |
6 7/8 - 7 |
|
M |
57-58 |
22 1/4 - 22 3/4 |
7 1/8 - 7 1/4 |
|
L |
59-60 |
23 - 23 1/2 |
7 3/8 - 7 1/2 |
|
XL |
61-62 |
23 3/4 - 24 1/4 |
7 5/8 - 7 3/4 |
|
XXL |
63-64 |
24 3/4 - 25 |
7 7/8 - 8 |
The helmet size measurement will correspond to a particular size in the model range you are interested in. This is a good starting point if you want to buy a particular brand or model.
Although human heads have an infinite variety of shapes and sizes, most of us fall into these two categories:
Some of us may have a combination of these two head shapes. It's possible to have combinations of these shapes in an infinite number of variations.
Fortunately many motorcycle helmets are manufactured with internal shapes that roughly match these "oval" or "round" shaped head categories.
Below are illustration of exaggerated human head shapes that is viewed from front or back of the head

Why is it important to know your head shape?
It's important to know your head shape because you can roughly know which helmet brand and model will fit by matching your head shape to the helmet's internal shape. Not every helmet will fit the same and almost every helmet brand and model is different. Shape is one of the most important factors to understand when purchasing a motorcycle helmet.
Lower end helmet
Lower end motorcycle helmet manufacturers tend to produce helmets with a generic shape that will fit most of the customers. The thickness of helmet inner lining, helmet cushion and cheek pads are the components that will make a difference to your fit.
Higher end helmet
Arai is the only high end motorcycle helmet manufacturer that have developed motorcycle helmet models that are specifically engineered to fit different head shapes.
Summary
Always remember - there are different helmets are produced in a range of sizes to satisfy a mass market. Your head shape and size are unique to you, so take your time to use the above tips when selecting your new motorcycle helmet.