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Hat size: find your size from your head measurement

Convert your head circumference into US fitted, UK, European and letter (S, M, L, XL) hat sizes for caps, fedoras, beanies and helmets.

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European size (cm)

57

US fitted size

7.125

7 ⅛
UK size
7.000
7
Letter size
3
M (57–58 cm)
Head circumference in inches
22.50 in

One measurement, several sizing systems

Hats are sized by head circumference, but each country expresses it differently. Europe uses centimeters, the United States uses a fitted size that looks like a diameter in inches, the United Kingdom uses the US scale shifted by one eighth, and many caps and beanies simply use letters. This calculator converts one measurement into all of them.

How to measure

  1. Use a soft tape measure, or a piece of string that you then measure against a ruler.
  2. Wrap it around your head about ⅛ inch (3 mm) above the eyebrows and the tops of the ears, across the widest part of the back of the head.
  3. Keep it level and snug, as a hat would sit, without pulling tight.
  4. Measure two or three times and use the largest value. Thick hair, braids or a hairstyle you usually wear under the hat all count.

The formulas

US fitted size ≈ circumference in inches ÷ π, rounded to the nearest eighth

UK size = US size − ⅛

European size = circumference in centimeters, rounded to the nearest centimeter

Example

A head circumference of 22½ inches (57.2 cm):

  • US: 22.5 ÷ 3.1416 = 7.16, so 7⅛
  • UK: 7
  • European: 57
  • Letter size: M

Size chart

Circumference (in) Circumference (cm) US UK Letter
21⅝ 55 6⅞ 6¾ S
22 56 7 6⅞ S
22⅜ 57 7⅛ 7 M
22¾ 58 7¼ 7⅛ M
23⅝ 60 7½ 7⅜ L
24 61 7⅝ 7½ XL

Brands vary, especially for letter sizes, so check the maker’s chart when one is available.

Fit tips

  • Between sizes: choose the larger one. A hat that is slightly big can be adjusted with sizing tape inside the sweatband; one that is too small cannot be stretched much.
  • Felt and straw hats keep their size; knits and stretch-fit caps cover a range of sizes.
  • Helmets for cycling, skiing or motorcycling use the same circumference measurement but their own size ranges; follow the manufacturer’s chart and safety fitting instructions.
  • Children’s heads grow fast, about 2 cm in the first months of life and more slowly afterward, so measure again each season.

Frequently asked questions

How do I measure my head for a hat?

Wrap a soft tape measure around your head just above the eyebrows and ears, across the widest part at the back. Keep it snug but not tight. Measure twice and use the larger value, or round up if you are between sizes.

How are US hat sizes calculated?

A US fitted hat size is roughly the head circumference in inches divided by π, rounded to the nearest eighth. A 22½-inch head gives 7⅛. UK sizes run one eighth smaller, so the same head is a UK 7.

What size is a European hat?

European and French sizes are simply the head circumference in centimeters, such as 57 or 58. Letter sizes vary by brand, but M usually fits 57 to 58 cm and L 59 to 60 cm.

Should a hat be tight?

A fitted hat should sit comfortably without leaving a red mark on your forehead. Felt and straw hats do not stretch much, while knit beanies and adjustable caps fit a wide range. Hat size reducer tape can fill a small gap.

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Results are estimates provided for information purposes. They do not replace professional advice.

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