A bicycle helmet needs to fit the person wearing it, not simply match the printed size or look right on a shelf. Take time to position it, adjust the straps according to its instructions, and check that it stays snug and level before riding. A shop or qualified instructor can help if the fit remains unclear.
Choose a helmet intended for cycling and meeting the applicable standard where you use it. For the United States, look for the appropriate CPSC compliance labeling. Do not assume that a helmet designed for another activity provides the same protection.
Start with size and position
NHTSA's fitting guidance places the helmet level on the head and low on the forehead, about one or two finger-widths above the eyebrows. It should not be tipped backward to expose the forehead or pushed so low that it interferes with seeing.
Use the maker's sizing and adjustment instructions for the model. If you cannot obtain a stable, comfortable fit, try a suitable different size or shape with help. Tightening straps is not a substitute for a helmet that fits the head properly.
Arrange the straps deliberately
Adjust the side straps to form a V around each ear, following the manufacturer's directions for its adjusters. Buckle the chin strap and make it snug. NHTSA's check allows no more than one or two fingers under the strap.
Use a mirror or ask someone to help. Make the adjustments while stationary, not as you roll away. Keep loose strap ends managed as the instructions show rather than improvising a fastening that interferes with the buckle.
Recheck after everything is adjusted
Confirm that the helmet remains level and does not move excessively when you check it as directed. If it rocks backward or forward, review the position and strap adjustment. Do not solve one loose area by pulling another part until the whole arrangement becomes uncomfortable.
If you wear glasses or another item with the helmet, check that they work together without disturbing the fit. Follow the maker's instructions about anything worn underneath. A previously useful adjustment may need rechecking when the arrangement changes.
Keep condition and fit as separate checks
A helmet can fit and still need replacement because of damage or an impact. The CPSC's helmet guidance and the manufacturer's instructions can help you understand appropriate use, care, and replacement. Follow those rather than deciding only from how the outside looks.
If the helmet's history or condition is uncertain, seek appropriate advice before using it. Do not add unapproved parts, drill holes, or make a modification to force a fit.
Make fitting part of getting ready
Before each ride, put the helmet on correctly and check the fastening. If several people share storage, make sure you have picked up the helmet adjusted for you. Keep it where it will not be casually damaged between outings.
A correctly fitted helmet is one part of preparing for cycling. Keep the bicycle in working order, choose an appropriate route, and use the riding skills and traffic awareness the outing requires. Finish the adjustment before moving, so the ride begins with the equipment already ready.