How to choose a bike helmet

Few people would choose to ride in a car with no seat belts. So why hop on a bike without a bike helmet?

Helmets simply make sense in all riding conditions. At least 21 states and Washington, D.C., even have laws requiring them.

Here are some tips for choosing a bike helmet model that is well-suited to your needs.

Which Type? Sport, Road or Mountain?

Cycling helmets come in 3 basic styles: sport (also called multi-use), road and mountain. All types are designed to protect a rider's head from impact while being lightweight and comfortable. The differences:

  • Sport (multi-use) helmets ($35-$60): An economical choice for recreational, commuter, road and mountain bikers; also popular with skateboarders and inline skaters.
  • Road bike helmets ($60-$250): Preferred by roadie enthusiasts for their low weight, generous ventilation and aerodynamic design.
  • Mountain bike helmets ($35-$200): Designed to ventilate well at low speeds; distinguished by their visors, enhanced rear-head coverage and a firm, secure fit for tackling rough terrain. Often used by cyclocross riders, too.

Shop REI's selection of bike helmets.

Find the Right Size

A good fit is vital. Multi-use helmets usually offer a single, adjustable size. Most others come in small, medium, large or extended sizes.

To find your size, wrap a flexible tape measure around the largest portion of your head—about 1" above your eyebrows. Or, wrap a string or ribbon around your head, then measure the length of string with a straight-edge ruler or yardstick.

Look for a helmet size that matches your measurement. On, the size range is listed under the "Specs" tab on each product page.

General sizing parameters for adults:

  • Small: 20"-21.75" (51cm-55cm)
  • Medium: 21.75"-23.25" (55cm-59cm)
  • Large: 23.25"-24.75" (59cm-63cm)
  • Extra-small, extra-large: Below 20" (51cm), above 24.75 (63cm)
  • One size fits all (men): 21.25"-24" (54cm-61cm)
  • One size fits all (women): 19.75"-22.5" (50cm-57cm)

Most kids' helmets are one-size-fits-all with a range of 18"-22.5" (46cm-57cm). Some adults with smaller heads can wear these comfortably.

Between sizes? Opt for the smaller size.

Adjust Helmet Fit

Adjustment dial

Almost all helmets offer a universal-fit sizing wheel on the back of the helmet's internal sizing ring. Chinstraps are adjustable, too. A few helmets, most often kids' models, offer a selection of internal pads to fine-tune the fit.

To adjust the fit, first expand the sizing wheel before you place a helmet on your head. Once the helmet is in place, reach behind your head and tighten the ring (usually by twisting a dial) until you achieve a snug fit.

A good-fitting helmet should be snug but not annoyingly tight. It should sit level on your head (not tilted back) with the front edge no more than 1" (a width of approximately 2 fingers) above your eyebrows so that your forehead is protected. Push the helmet from side to side and back to front. If it shifts noticeably (1" or more), adjust the sizing wheel (or pads) to snug the fit.

Next, buckle and tighten the chinstrap. Push up on the front edge of the helmet, then up on the back edge. If the helmet moves significantly in either direction (more than 1"), tighten the chinstrap and try again. The straps should form a "V" as they rest under each ear. Adjust the straps around both ears to achieve a comfortable fit.

Finally, with the chinstrap buckled, open your mouth. The helmet should press against your forehead as you do so. If not, tighten further and repeat. Just don't overtighten the strap until it's uncomfortable.

Note: Nutcase-brand helmets (multi-use) use a magnetic chinstrap attachment instead of a buckle. This can help adults with physical limitations (or kids) to securely fasten their chinstrap.

Components of a Helmet

  • Liner: Most helmet liners are made of expanded polystyrene foam. On impact, the liner dissipates the force of the impact to protect your head. Make sure the liner fits your head comfortably and that it's not damaged or dented.
  • Shell: Most cycling helmets are covered with a plastic shell to hold the helmet together in a crash, provide puncture-resistance and allow the helmet to slide on impact (to protect your head and neck). Make sure the shell is intact and in good shape.
  • Construction: In-mold construction is a popular process that fuses the outer shell and inner foam without the use of glues. This results in light yet strong designs.
  • Ventilation: Helmet vents enhance wind-flow over your head, keeping you cooler and more comfortable as you ride. The more vents you have, the lighter the helmet, too.
  • Straps: The strap system should be comfortable and easy to take on and off. Look for beefier straps for rough terrain and mountain trails, lighter and cooler straps for road riding.
  • Hair port: Some helmets come with a strap design that accommodates ponytails.

Comparing the Specs

Each helmet description on includes some or all of the following specifications:

Weight: Almost always listed in grams (28.34g = 1 oz.). While weight is not a big concern for occasional cyclists, racers and frequent riders really appreciate the weight savings of a lighter helmet.

Tip: The price usually goes up as the weight comes down.

Vents: Designed to create airflow around and over your head. The more vents, the cooler the head (and the pricier the helmet).

Visor: Some riders prefer having a sun-shielding visor attached to their helmet. It does, however, add a fractional ounce of weight and slight wind resistance.

Fit system: Manufacturers create a variety of names (e.g., Roc Loc, GPS, Acu-Dial) to represent their approach to a helmet's sizing wheel (usually a dial). For a detailed explanation, visit the manufacturer's website.

Impact Certification

By law, all helmets sold in the U.S. must meet standards set by the Consumer Products Safety Commission (CPSC). Some helmets are also endorsed by the nonprofit Snell Foundation, but the CPSC stamp of approval is what matters.

Test results have helped manufacturers create helmets that are light, comfortable and able to handle significant impacts.

To Wear or Not to Wear?

Regardless of helmet laws, there are impassioned supporters and opponents of bicycle helmet use. However, the statistics speak for themselves.

According to the Insurance Institute for Highway Safety’s report for bicycle fatalities, on average less than 2% of motor vehicle crash deaths involve bicyclists. In 2010, 89% percent of those killed were age 16 and over; the majority sustained serious injuries to the head

In 2009, 91% percent of bicyclists killed were not wearing helmets.

Not surprisingly, helmet use has been estimated to reduce head injury risk by 85%.

So, though wearing a helmet doesn’t protect one against all injuries, studies (and anecdotal evidence) do suggest that many head, skull and brain injuries (many fatal) can be prevented or minimized with helmet use at the time of a crash.

For more information, visit the Bicycle Helmet Safety Institute.

When to Replace a Helmet

Speaking of crashes, any helmet involved in an accident is likely to get damaged. Replace the helmet after any significant impact, even if everything looks OK.

If you've been crash-free, it is generally recommended to replace your helmet after 5 years. Pollution, UV light and weathering can weaken its components over time.

A few helmet tips:

  • Avoid using chemical solvents to clean a helmet. Manufacturers recommend only the use of a soft cloth or sponge, plus mild soap and water.
  • Do not store a helmet in an attic, garage, car trunk or other area where heat can accumulate. Excessive heat may cause bubbles to form on helmet parts. Do not wear a heat-damaged helmet.
  • Avoid loaning your helmet to others. You want to know exactly what kind of use your helmet has experienced during its lifespan.

Shop REI's selection of bike helmets.