Inches to hat size chart
Each fitted size covers about ⅜ of an inch of head circumference. The chart shows the inch measurement in both fractions and decimals so you can match a tape measure that reads either way.
| Inches | cm | US | Letter |
|---|---|---|---|
| 19 ⅝ (19.7) | 50 | 6 ¼ | – |
| 20 ⅛ (20.1) | 51 | 6 ⅜ | – |
| 20 ½ (20.5) | 52 | 6 ½ | XS |
| 20 ⅞ (20.9) | 53 | 6 ⅝ | XS |
| 21 ¼ (21.3) | 54 | 6 ¾ | S |
| 21 ⅝ (21.7) | 55 | 6 ⅞ | S |
| 22 (22) | 56 | 7 | M |
| 22 ½ (22.4) | 57 | 7 ⅛ | M |
| 22 ⅞ (22.8) | 58 | 7 ¼ | L |
| 23 ¼ (23.2) | 59 | 7 ⅜ | L |
| 23 ⅝ (23.6) | 60 | 7 ½ | XL |
| 24 (24) | 61 | 7 ⅝ | XL |
| 24 ⅜ (24.4) | 62 | 7 ¾ | XXL |
| 24 ¾ (24.8) | 63 | 7 ⅞ | XXL |
| 25 ¼ (25.2) | 64 | 8 | 3XL |
| 25 ⅝ (25.6) | 65 | 8 ⅛ | 3XL |
| 26 (26) | 66 | 8 ¼ | 3XL |
The formula
Fitted size = head circumference in inches ÷ 3.1416, rounded to the nearest ⅛. A 23 ½ inch head is 23.5 ÷ 3.1416 = 7.48, which is 7 ½. To go the other way, multiply the fitted size by 3.1416 to get inches, then by 2.54 to get centimetres.