Take several measurements to get the largest part of your head

If you do not have a cloth measuring tape, a piece of string can be used. Wrap the string around your head and mark where the ends meet. Lay the string on a regular measuring tape to determine the measurement.

Many helmet manufacturers give their helmet sizes in centimeters, so you may need to convert this measurement into a metric dimension.

The measurement will give you a starting point for selecting a helmet size. Because head and helmet shapes vary, a measurement alone will not guarantee a good fit. It is best to try on a variety of helmets from different manufacturers. A size small from one manufacturer may crush your head, while another’s extra small is just right.

The effect of head and helmet shape cannot be under emphasized. When you measure your head, also note your general head shape: is it round, oval, egg-shaped or reverse egg-shaped? Manufacturer’s like Arai, for example, have specific helmet lines designed for each head shape.

It is important to try on helmets before you purchase. It is only pure luck to purchase one that fits well based on only your head measurement. If you’re buying mail order, make sure that you can return your purchase if it does not fit properly.

When you go to a store, begin by selecting a helmet that meets your general criteria for style. We’ll assume that you’re only considering a full faced helmet, since anything less is not recommended from a safety perspective. Next try on a helmet that seems to be a likely fit based on the measurement.

Pick out a size smaller than you think you’ll need and one that is a size larger. As you try on the helmets, you should run through the following tests with each candidate before purchasing.

To test the general fit, put the helmet on and push down on the top of the helmet to seat it on your head. It should fit snugly and firmly against your head. The helmet cheek pads should touch your cheeks and there should be no gaps between the helmet and your temples. If it doesn’t fit firmly, the cheek pads don’t touch your cheeks or there are gaps try the next size smaller.

There should be no gaps at the temples or cheeks

Gaps at the temple may mean this helmet is the wrong shape for your head. If the size smaller doesn’t fit either, try another model or brand of helmet.

In a crash your helmet is subject to forces that are much greater than you can imagine. This next set of steps are designed to make sure that your helmet stays in place and does its job when your head hits the pavement.

With the chin strap secured, grab the helmet on each side of the chin bar and try moving the helmet side-to-side. Your checks should move with the helmet as you move it. If the helmet moves without moving your checks, it is too big or the wrong shape.

Push on the front of the helmet in the middle of the chin bar. The helmet should not come away from your head in the back and the chin bar should not touch your mouth or nose.

No helmet should ever fail this next test: with the helmet securely fastened, grab the back of the helmet and try to roll it over your head and off. This may sound extreme, but helmets that are too large can actually come off this way and will surely come off in an accident. If your helmet has passed all of these tests, wear it around the store for a 30 minutes or so. During this time, check to make sure your eye glasses will fit inside the helmet and visor will close properly. As you wear the helmet around, you shouldn’t notice any pressure points.

If you are not used to a full faced helmet wearing the helmet in the store may seem restrictive. This is somewhat like wearing a diving mask around in your living room – it’s never going to feel completely right. When you’re riding there is significantly more air flowing through your helmet and it will not feel cumbersome.

When you remove the helmet you shouldn’t have a headache or have red marks on your head.

Finding a properly fitting helmet can be time consuming, but this will be worthwhile if you ever need to use the helmet to save your life or your basic motor or cognitive skills. Don’t forget that most riders will choose a helmet that is too large or the wrong shape – don’t be afraid to keep trying smaller helmets until you find one that truly fits.