Hat Size Converter
Fitted caps, fedoras, and helmets all size by head circumference, not by small, medium, or large. Enter your head measurement in centimeters or inches and the converter returns your hat size in the US, UK, and EU systems.
Hat Size Converter
Enter your head circumference in centimetres or inches to get your US, UK and EU hat size.
Result
How to measure your head for a hat
- Use a soft tape measure (or a string, then measure the string against a ruler).
- Wrap it around your head about half an inch above your eyebrows and ears, where the hat’s sweatband will sit.
- Keep the tape level all the way around, snug but not tight.
- Measure two or three times and use the largest reading.
- If your measurement falls between two hat sizes, go up to the larger size.
US hat size is your head circumference in inches divided by pi, rounded to the nearest eighth (the hatters’ formula). UK runs one eighth smaller than US by the traditional convention, and EU is the circumference in centimetres. Spot-checked against New Era’s published 59FIFTY fitted chart (7 = 22 in / 55.8 cm, 7 1/2 = 23 1/2 in / 59.6 cm) and cross-checked with independent hat charts. Note two honest caveats: New Era itself prints the same number for US and UK on its fitted caps, so some shoppers treat them as equal; and brands vary (Stetson’s 7 1/8 sits a quarter inch larger than New Era’s). When between sizes, size up.
How to use the converter
- Choose your unit: centimetres or inches. Use whichever your tape measure shows; the converter handles both.
- Wrap a tape around your head about half an inch above your eyebrows and ears, where a hat’s sweatband sits. Enter the number.
- Press Convert. The result shows your US, UK, and EU hat size, ready to match against a size chart.
Understanding your result
US hat size is your head circumference in inches divided by pi, rounded to the nearest eighth: the traditional hatters’ formula. UK runs one eighth smaller than US by convention, and EU is simply the circumference in centimetres, rounded to the nearest whole number.
If your measurement falls between two sizes, the tool rounds to the nearest eighth and advises sizing up. A slightly loose hat can be adjusted with sizing tape; a tight hat only gets more uncomfortable through the day.
Worked example
A shopper measures 23.5 inches around their head. They choose inches, enter 23.5, and press Convert. The result: US 7 1/2, UK 7 3/8, EU 60. This matches New Era’s published 59FIFTY fitted chart, which lists 7 1/2 for a 23 1/2 inch head, so they order the 7 1/2 with confidence.
Last reviewed: October 2026.
Frequently asked questions
Where exactly do I measure my head?
About half an inch above your eyebrows and ears, where a hat’s sweatband will sit. Keep the tape level all the way around, snug but not tight. Measure two or three times and use the largest reading: heads are rarely perfectly round, and the largest reading is the one the hat must clear.
Are US and UK hat sizes the same?
Not by the traditional convention, where UK runs one eighth smaller than US. But many brands, including New Era on its fitted caps, print the same number for both. This converter follows the traditional offset and discloses it, so compare the underlying inches or centimetres when a brand’s chart looks different.
What is EU hat size based on?
Head circumference in centimetres, rounded to the nearest whole number. It is the most literal system: a 60 cm head is an EU 60. The converter accepts centimetres directly, so EU sizing needs no formula at all.
My measurement is between two sizes. Which do I pick?
Size up. Between-size heads round to the nearest eighth, and a hat that is slightly loose can be adjusted with sizing tape, while a tight hat only gets more uncomfortable. This is one case where rounding up is the safe default.
Why does the same size fit differently in different brands?
Crowns are cut on different blocks, just as shoes are built on different lasts. A 7 1/2 from one maker can sit a quarter inch larger than another’s. The converter translates the numbering; the brand’s own chart translates the cut.