Hat Size Converter
Convert hat sizes between US, UK, EU, and head circumference in cm and inches.
Covers baseball caps, fedoras, beanies, and formal hats.
Type in any field — the others update instantly.
Hat sizes are based on head circumference, but each region uses a different scale.
US hat sizes are based on the diameter of a circle with the same circumference.
- US size = circumference (inches) / π (3.14159)
UK hat sizes use the same system as US sizes.
EU hat sizes equal the head circumference in centimeters.
Conversion formulas:
- 1 inch = 2.54 cm (exact)
- US/UK size = circumference in inches / π
Common hat sizes:
| US/UK | EU | Circumference (cm) | Circumference (in) |
|---|---|---|---|
| 6-3/4 | 54 | 54 cm | 21.3" |
| 6-7/8 | 55 | 55 cm | 21.7" |
| 7 | 56 | 56 cm | 22.0" |
| 7-1/8 | 57 | 57 cm | 22.4" |
| 7-1/4 | 58 | 58 cm | 22.8" |
| 7-3/8 | 59 | 59 cm | 23.2" |
| 7-1/2 | 60 | 60 cm | 23.6" |
| 7-5/8 | 61 | 61 cm | 24.0" |
| 7-3/4 | 62 | 62 cm | 24.4" |
Measure around the widest part of your head, just above the ears.
EU sizing is once again the sensible one, because the number is just your head circumference in centimeters: measure 58 cm around and you’re an EU 58. The US and UK scale is quirkier, defined as the diameter of a circle with your head’s circumference, which is why the formula divides by pi and the sizes climb in eighths of an inch, roughly a centimeter per step. That’s also why US hat numbers look like odd fractions, 7-1/8 and 7-1/4, rather than tidy round figures.
Measuring is where fit is won or lost. Run a soft tape, or a string you then lay against a ruler, around the widest part of the head about a finger above the ears and across the mid-forehead, and keep it snug rather than tight. A couple of practical notes: heads are usually slightly oval, so a structured fitted hat can pinch front-to-back even at the “right” circumference, which is why adjustable and stretch-fit styles forgive a lot. Felt and wool hats also give a little with wear, so when you’re between sizes on a quality hat, the smaller one often breaks in to a perfect fit.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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