How to Size a Bike Helmet for a Secure Fit
By Dakine | Backpacks, Luggage, Surf, Snow, & Bike Gear Since ... | Published: 2026-10-18
Category: How-to Guides
Learn how to measure your head and choose a bike helmet that fits snugly and safely. Step-by-step guide with common mistakes to avoid.
Quick Answer
To size a bike helmet, measure the circumference of your head just above your eyebrows, then match it to the manufacturer's size chart. A secure fit means the helmet sits level, doesn't move when you shake your head, and the chin strap is snug but comfortable.
Why a Proper Fit Matters More Than Price
A helmet that's too loose can shift during a crash, leaving your forehead or temples exposed. One that's too tight can cause headaches and might tempt you to wear it unbuckled. A properly sized helmet distributes impact forces more evenly and stays in place when you need it most.
Even the most advanced protective technology won't work if the helmet doesn't fit correctly. That's why taking a few minutes to measure your head is worth it—it's the first step to real protection.
Understanding Helmet Sizing Systems
Most bike helmets use a universal sizing system based on head circumference in centimeters. However, sizes can vary slightly between brands, so always check the specific size chart for the helmet you're considering. For example, Dakine's Slayer MIPS Helmet and Slayer Helmet both come in multiple sizes, and each has its own size chart.
A common mistake is assuming your hat size matches your helmet size. Hat sizes are often based on different measurements and can be less precise. Always measure your head fresh, and if you're between sizes, choose the smaller one—a helmet that's slightly snug can be adjusted, but one that's too loose can't be fixed.
Step-by-Step Helmet Sizing Guide
- Measure your head: Use a flexible tape measure. Wrap it around your head, about one inch above your eyebrows and ears, where the helmet will sit. Keep the tape level and snug, but not tight. Record the measurement in centimeters. If you don't have a tape measure, use a string and then measure it against a ruler.
- Check the size chart: Compare your measurement to the helmet's size chart. For Dakine Slayer helmets, the chart lists head circumference ranges for each size. If you're between sizes, go with the smaller one—you can always adjust the fit system. Don't rely on the size printed on the box; always measure your head for each helmet you try.
- Try the helmet on: Place the helmet on your head and adjust the fit system (usually a dial at the back) until it feels snug. The helmet should sit level on your head, about two finger widths above your eyebrows. It should not rock side to side or front to back. Shake your head gently—if the helmet shifts, tighten the fit system or try a smaller size.
- Adjust the straps: Fasten the chin strap and adjust the side straps so they form a 'V' around your ears. The chin strap should be snug but allow you to open your mouth comfortably. The buckle should sit flat under your chin. A common mistake is leaving the straps too loose; the helmet should stay put even when you open your mouth wide.
- Do the final fit check: With the helmet on and straps fastened, try to push the helmet forward and backward. It should not move more than about an inch. Also, check that the front edge is not too high or too low—it should protect your forehead without blocking your vision. If the helmet moves, re-adjust the fit system and straps; if it still moves, try a different size.
Helmets That Fit Right
- Slayer MIPS Helmet: The Slayer MIPS Helmet includes MIPS (Multi-directional Impact Protection System) and a size chart for precise fitting. MIPS adds an extra layer of protection against rotational forces, and using the size chart ensures the helmet sits correctly to take full advantage of it.
Slayer MIPS Helmet - Slayer Helmet: The Slayer Helmet features ERT (Energy Reduction Technology) and also comes with a detailed size chart. ERT is designed to reduce impact energy, but only when the helmet fits snugly—so measuring your head is key to getting this benefit.
Slayer Helmet
