Position the tape
Wrap it level around the widest circumference without pulling tightly.
Measure carefully, identify a likely size band and then check the exact size chart for the offered helmet model.
Use a flexible measuring tape around the widest part of the head. Keep it level, usually around one to two finger widths above the eyebrows and above the ears.
Wrap it level around the widest circumference without pulling tightly.
Take the measurement twice. Use the larger consistent reading when the values differ slightly.
Compare the result with the manufacturer chart for the specific model, not a generic S/M/L assumption.
The helmet should sit level and stable. Straps and retention systems must be adjusted according to the instructions.
Generic bands overlap and vary by model. A 57 cm measurement may fall into different labelled sizes across manufacturers. Request the exact chart before ordering, especially for children or mixed-size bulk orders.