How to use the hat size calculator
- Wrap a soft tape measure around your head just above your eyebrows and ears (about 1 cm or ½ inch), over the widest part at the back. Keep it level and snug, not tight.
- Enter the figure in Head circumference (cm) or Head circumference (inches). The other box fills in, and decimals such as 57.5 work.
- Read US size, UK size, EU size and Letter size. The matching row of the chart is highlighted.
- Already know your size? Pick it in Or pick a US size to see the head measurement it fits.
How hat sizes are worked out
A US fitted hat size is the diameter of a round head with the same circumference as yours: head circumference in inches ÷ π, rounded to the nearest ⅛. Because 2.54 × π is almost exactly 8, you can also divide centimeters by 8, so 56 cm ÷ 8 = 7. The EU size is simply the circumference in centimeters. Most charts list the UK size one eighth below the US size (US 7 = UK 6⅞), which is what this tool shows, but some makers use their own scale, so compare centimeters when ordering. Letter sizes follow the Stetson chart: XS 52 to 53 cm, S 54 to 55, M 56 to 57, L 58 to 59, XL 60 to 61, XXL 62 to 63 and 3XL 64 to 65.
Worked example with the default values
With 56 in Head circumference (cm), the inches box shows 22 (56 ÷ 2.54 = 22.05). The tool divides 22.05 by π to get an exact size of 7.018, and the nearest eighth is 7. The boxes read US 7, UK 6⅞, EU 56 and M, and the 56 cm row of the chart is highlighted.
Between sizes and other limits
If you land between two sizes, choose the larger one: a slightly roomy hat can be padded, while a tight one gives you a headache. Measurements from 49.4 to 66.3 cm are accepted, which is US 6¼ to 8¼. Hair volume, thick hair and a hat's own sweatband all change the fit, so measure twice. Stretch caps and beanies are often sold as S/M or L/XL, which use these letter ranges loosely, and letter sizes differ between brands.
Converting between centimeters and inches for something else? Use the length converter. Buying other sized items, the shoe size converter and the ring size converter work the same way.
Sources: Wikipedia, Hat size; Stetson hat sizing assistant.
Hat size FAQ
How do I measure my hat size?
Wrap a soft tape measure around your head just above your eyebrows and ears, over the widest part at the back. Keep it level and snug, then enter the centimeter or inch figure in the calculator above.
What hat size is 22 inches?
A 22 inch head is 55.9 cm, which is US 7, UK 6⅞, EU 56 and medium.
What size is a 58 cm hat?
A 58 cm head is 22.8 inches, which is US 7¼, UK 7⅛, EU 58 and large.
What is a 7⅜ hat in cm?
About 59 cm, or 23.2 inches. A 7⅜ hat has a 7.375 inch diameter, and 7.375 × π = 23.17 inches around, which is 58.8 cm.
What do S, M, L and XL mean for hats?
Roughly, S is 54 to 55 cm (US 6¾ to 6⅞), M is 56 to 57 cm (7 to 7⅛), L is 58 to 59 cm (7¼ to 7⅜) and XL is 60 to 61 cm (7½ to 7⅝). Brands differ, so check the maker's chart.