A fitted hat should sit level on the head, snug enough to stay put in the wind and loose enough not to leave a mark. Hat sizes are tied to the circumference of the head, but the numbers look odd: a US size 7 1/4 is the same as a 58 cm head and a UK 7 1/4. This calculator turns your head circumference into the US, UK and European hat size and the Small to XX-Large band.
How to use the hat size calculator
- Measure your head. Place a soft tape about an eighth of an inch above your ears and across the middle of the forehead, keeping it level around the back.
- Enter the circumference in centimetres or inches.
- Read the size. The result shows US, UK and EU sizes and the band (Small to XX-Large). The calculator rounds a value between two sizes up to the next one.
Hat size formula
US size ≈ circumference (in) ÷ π = circumference (cm) ÷ 7.98
between sizes → take the larger size
The Sizely hat size chart states that the EU size equals the head circumference in centimetres on every row and that the US size equals the circumference in inches divided by π, rounded to an eighth. Its centimetre-to-US pairs match the Stetson hat size conversion for every size from 53 to 64 cm, so the lookup below uses them (both retrieved 2026-10-15). The inch column is the Sizely chart’s own figure.
| EU (head, cm) | Head (in, chart) | US | UK | Size band |
|---|---|---|---|---|
| 53 | 20 1/2 | 6 5/8 | 6 1/2 | Small |
| 54 | 21 1/4 | 6 3/4 | 6 5/8 | Small |
| 55 | 21 5/8 | 6 7/8 | 6 7/8 | Small |
| 56 | 22 | 7 | 7 | Medium |
| 57 | 22 1/2 | 7 1/8 | 7 1/8 | Medium |
| 58 | 22 7/8 | 7 1/4 | 7 1/4 | Medium |
| 59 | 23 1/4 | 7 3/8 | 7 3/8 | Large |
| 60 | 23 5/8 | 7 1/2 | 7 1/2 | Large |
| 61 | 24 | 7 5/8 | 7 5/8 | Large |
| 62 | 24 1/2 | 7 3/4 | 7 3/4 | X-Large |
| 63 | 24 7/8 | 7 7/8 | 7 7/8 | X-Large |
| 64 | 25 1/4 | 8 | 8 | XX-Large |
| 65 | 25 5/8 | 8 1/8 | 8 1/8 | XX-Large |
Worked example
A head measures 57.2 cm around.
- 57.2 cm falls between the 57 cm and 58 cm rows, so it rounds up to 58 cm.
- US size: 7 1/4, UK size: 7 1/4, EU: 58.
- The size band is Medium.
- Check by formula: 57.2 ÷ 2.54 = 22.52 in; 22.52 ÷ π = 7.17, which is between 7 1/8 and 7 1/4, so going up gives 7 1/4.
Choosing between hat types
- Fitted hats (fedoras, flat caps, fitted baseball caps) are sold in exact sizes, so measure carefully.
- S/M/L hats cover a band of sizes; pick the band shown in the result. Straw hats may shrink or stretch slightly with moisture.
- Adjustable caps cover most heads, but a very small or large head may be outside the range.
- Winter hats with thick liners may need half a size more than the measurement.
Sources disagree on the UK size for some entries, as noted in the table, and each brand uses its own last. Use the brand’s chart where one is given. For other accessories see the Glove Size Calculator and Ring Size Calculator. This page gives general sizing information.
Sources
Every figure above comes from these pages, read directly on the dates shown.
- Sizely — hat size chart (US, UK, EU, inches, cm) — checked 2026-10-15
- Stetson — size chart: hat size conversion (US size, inches, cm) — checked 2026-10-15
Frequently asked questions
How do I measure my head for a hat?
Wrap a soft tape around your head about 1/8 inch (a few millimetres) above your ears and across the middle of your forehead, level all the way round. Pull it snug but not tight, and read the number.
What if I am between two hat sizes?
Go up. Both the Stetson and Sizely charts say to order the larger size when your measurement falls between two sizes. The calculator rounds the centimetre value up to the next whole centimetre for this reason.
How is hat size related to head circumference?
The US size is the circumference in inches divided by π, and the EU size is the circumference in centimetres. A 56 cm head is 22.05 inches around, and 22.05 ÷ π is about 7.0.
Why do UK and US hat sizes differ?
On the Sizely chart they match from size 7 up, and the UK size runs one eighth smaller below 7. Some makers treat the UK size as one eighth smaller than the US across the range, so check the chart of the brand you are buying.
Are baseball cap sizes the same?
Fitted caps use the same head-circumference scale but come in whole-eighth sizes, and S/M/L caps cover a band of sizes. Use the band shown in the result as a guide. See also Glove Size Calculator.