cm to US Helmet Size Conversion
| Head (cm) | US Size |
|---|---|
| 54-55 | S |
| 56-57 | M |
| 58-59 | L |
| 60-61 | XL |
Sizing conventions vary by brand and by cut — this table shows the standard published conversion. Always check the garment's own size chart when one is available. See how these tables are compiled.
Helmet sizing is measured head circumference in centimetres worldwide, so a 58cm head converts to a US 'L' on the standard chart — this is a labelling lookup more than a genuine unit conversion, since the underlying measurement never changes.
Because helmet safety depends on a snug, correctly-sized fit, measuring your own head circumference with a soft tape directly (wrapped just above the eyebrows) and matching it to the centimetre range on this chart is more reliable than assuming a size from a different brand's helmet you already own.
Frequently asked questions
Why is helmet sizing 'converted' if it's already in centimetres?
Because most retailers still label the size with a letter (S/M/L) rather than the raw centimetre figure — this page maps that letter back to the underlying head-circumference measurement it represents.