To figure out what size you wear, you will need to find a flexible cloth or bendable plastic tape measure (or, use a string that you can then lay flat and measure). Measure the circumference of your head at the place where you would wear a hat, typically about 1/4-1/2 inch above your ears and across the mid-forehead, completely circling your head. Take the measurement in inches and refer to the chart below. If you are in between two sizes, choose the bigger size -you can always add filler to larger hat to make it fit smaller.
| Head Size (up to) |
US Hat Size | CM | General Size |
| 21 1/4 - 21 5/8 | 6 3/4 - 6 7/8 | 54 - 55 | Small |
| 21 3/4 - 22 1/4 | 7 - 7 1/8 | 56 - 57 | Medium |
| 22 5/8 - 23 1/8 | 7 1/4 - 7 3/8 | 58 - 59 | Large |
| 23 1/2 - 24 | 7 1/2 - 7 5/8 | 60 - 61 | X-Large |
| 24 1/4 - 24 5/8 | 7 3/4 - 7 7/8 | 62 - 63 | XX-Large |
| 25+ | 8 | 64 | XXX-Large |
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