Wrap a soft tape around your head about 1 cm above the ears and eyebrows. That circumference is your size; US fitted sizes ≈ circumference in inches ÷ π (e.g. 57 cm ≈ 7 1/8).
| cm | inches | US fitted | Letter |
|---|---|---|---|
| 54 | 21.3 | 6 3/4 | S |
| 55 | 21.7 | 6 7/8 | S |
| 56 | 22.0 | 7 | M |
| 57 | 22.4 | 7 1/8 | M |
| 58 | 22.8 | 7 1/4 | L |
| 59 | 23.2 | 7 3/8 | L |
| 60 | 23.6 | 7 1/2 | XL |
| 61 | 24.0 | 7 5/8 | XL |
See the hat size converter.