Giro Bike Helmet Size Chart: How to Measure and Find Your Fit

By Caleb Morgan

Updated November 2026

A giro bike helmet size chart tells you which head circumference range matches each helmet size, but the chart only works if you measure your head correctly first. In this guide, you will measure your head in centimeters or inches, match that number to the right Giro size, and then test the fit on your head so you know the helmet will protect you on the road or trail. Think of the chart as a starting point and the fit check as the final word.

What a Giro Bike Helmet Size Chart Actually Measures

Giro helmets are sized by head circumference, which is the distance around your head just above your eyebrows and ears. Each size corresponds to a range, not a single number, and the ranges overlap slightly between sizes. That is why two riders with similar head sizes can sometimes fall on either side of a boundary and need to try both sizes.

Shopping for one? See our guide: Dirt Bike Helmet Size Chart: 10 Best Helmets Compared in 2026.

Giro publishes its size ranges on each product page and in its sizing information, and those ranges can differ between helmet models, especially between road, mountain, and youth lines. Always check the chart for the specific helmet you plan to buy rather than assuming one chart fits every Giro model. Manufacturers specify these ranges because the internal shell and padding shape vary from model to model.

Youth and adult sizes also use different ranges, so a child’s helmet will not match an adult chart. If you are shopping for a child, review the dedicated youth guide linked below before you measure.

For a broader look at how helmet charts from different brands compare, you can also read Bike Helmet Sizes Chart: How to Find Your Right Fit in 5 Steps, which walks through the same measuring logic across several brands.

Tools You Need Before You Measure

Measuring takes about two minutes, but a few simple items make the result far more accurate. Gather these before you start:

• A soft flexible tape measure, such as a sewing tape. A metal tape bends poorly around the head.
• A mirror, so you can check that the tape is level.
• A pen or your phone, so you can record the number right away.
• A second person if possible, which makes it easier to keep the tape level at the back.

If you do not have a flexible tape, a piece of string or a strip of paper works. Mark where the ends meet, lay the string flat against a ruler, and read the length.

Step-by-Step: How to Measure Your Head

Step 1: Position the Tape

Sit or stand upright with your head level and relaxed. Wrap the tape around your head about one centimeter (roughly half an inch) above your eyebrows and above your ears. The tape should sit low on the forehead, not up where a hat would sit higher.

Step 2: Keep the Tape Level

Check that the tape runs horizontally all the way around. A tilted tape adds length and can push you into a larger size than you need. Look in the mirror or ask someone to confirm the level.

Step 3: Tighten Without Compressing

Pull the tape snug, but not tight enough to press into your skin or flatten your hair noticeably. The measurement should reflect the true circumference of your head.

Step 4: Read and Record the Number

Note the measurement in centimeters if the chart uses them, or in inches otherwise. Take a second measurement to confirm. If the two readings differ by more than a few millimeters, measure a third time and use the most consistent result.

Step 5: Convert Units if Needed

Giro charts commonly list both systems, but if yours lists only one, convert carefully. One inch equals 2.54 centimeters, so a head circumference of 57 cm is roughly 22.4 inches. Round to the nearest tenth to avoid confusion.

Matching Your Measurement to the Giro Size Chart

Once you have your number, find the matching range on the chart for the exact helmet model you want. The table below shows the general structure used in adult sizing, but always confirm the current ranges on the product page, because they can change between model years.

Treat these ranges as a general illustration of how sizing bands are structured. Your final choice must come from the exact chart for the helmet you are buying, because Giro’s published bands vary by model.

If your number falls near the top or bottom edge of a range, you may fit either size. In that case, try on both if you can, or read the fit checks in the next section before deciding.

How to Check Fit on Your Head

A measurement gets you close, but fit is what protects you. A correctly sized helmet should feel firm and even, without pressure points, and it should stay in place when you shake your head.

1. Place the helmet level on your head, with the front edge about two finger-widths above your eyebrows.
2. Tighten the retention system at the back until the helmet feels snug all the way around.
3. Shake your head side to side and nod up and down. The helmet should move with your head, not slide back or tilt forward.
4. Buckle the chin strap and adjust it so it sits in a V shape under each ear, with the buckle centered under your chin.
5. Open your mouth wide. You should feel the helmet grip slightly. If it pulls off your head, it is too big.

If you feel a sharp pressure spot, especially at the temples or forehead, the helmet may be the wrong shape for your head even if the size seems right. Many riders find that a different model in the same size works better, because Giro shells vary in shape.

Factors That Can Change Your Fit

Hair and Head Covering

Thick or tightly braided hair can change how the helmet sits. Measure over the hair you will actually wear while riding, or measure with a thin cap if you plan to ride with one under the helmet.

Helmet Type

Road, mountain, and urban helmets may use different fit systems and shell shapes. A road helmet that fits well may feel different from a full-coverage mountain model, even in the same size on paper.

Padding Compression

Foam padding compresses slightly over the first few weeks of use. A helmet that feels perfect in the store may loosen a little over time, which is one reason to check fit before every ride.

Common Mistakes

• Measuring too loosely. A slack tape gives a larger number and can push you into a helmet that moves around in a crash.
• Using the wrong chart. Youth, adult, and different model lines have different ranges.
• Trusting the number alone. The chart narrows your choice, but the on-head fit check makes the final call.
• Ignoring the retention dial. Many Giro helmets rely on a rear dial, and an unadjusted dial can make a correct size feel loose.
• Skipping the fit check after buying online. If the helmet does not pass the shake test, return it and try another size.

Tips for a Better Fit

• Measure in the morning, when your head is usually at its normal size.
• Measure twice and average the results if the numbers differ.
• Check the helmet’s internal sizing pads, which some models include to fine-tune fit.
• Recheck the fit at the start of each season, since foam and straps wear over time.
• For a broader view of frame and fit planning on your bike, see Trek Bike Size Chart Cm: How to Pick Your Frame Size in Centimeters, which uses the same centimeter-based thinking.

Recommended gear

A flexible tape measure makes the first step easy and repeatable. Choose one with clear centimeter and inch markings so you can cross-check the Giro chart without converting numbers yourself. View on Amazon

A soft cloth tape is useful because it wraps evenly around the forehead and the back of the skull without pinching. View on Amazon

A small mirror helps you check that the tape sits level at the front and back, which is the step most people get wrong. View on Amazon

FAQ

Is the Giro bike helmet size chart the same for every model?

No. Giro publishes ranges for each helmet model, and those ranges can differ between road, mountain, and youth helmets. Always use the chart on the specific product page you are considering.

Which measurement should I use, centimeters or inches?

Use whichever unit the chart lists. If the chart shows both, pick one and stay consistent. Converting between them is simple: one inch equals 2.54 centimeters.

What if my measurement falls between two sizes?

Try on both sizes if you can. Choose the one that passes the shake and nod test without pressure points. If you buy online, check the return policy first.

Should I measure over my hair or without it?

Measure over the hair you will actually wear while riding. A tight braid or bun can change the number slightly.

How snug should a bike helmet feel?

It should feel firm and even, with no pressure points, and it should not move when you shake your head. It should not pull uncomfortably or leave deep marks after a ride.

Can a helmet get looser over time?

Yes. Foam padding compresses and straps stretch with use. Recheck the fit at the start of each season and adjust the retention system as needed.

Should I replace my helmet after a crash?

Yes. Manufacturers generally advise replacing a helmet after a significant impact, even if no damage is visible, because the internal foam may no longer protect as designed. If you have concerns about an injury, consult a medical professional.

Conclusion

A giro bike helmet size chart is most useful when you pair it with an accurate head measurement and a real fit check. Measure level, match your number to the chart for the exact model you want, and confirm the fit with the shake and nod test. Recheck the fit as the foam and straps settle in, and replace the helmet after any serious impact.

Related reading

• Giro Scamp MIPS Youth Bike Helmet Size Chart: How to Find the Right Fit

About Caleb Morgan

Caleb Morgan is part of our editorial team and reviews and edits our cycling for beginners guides, checking product details against manufacturer specifications and owner feedback.