About the Hat Size Calculator
This hat size calculator converts the circumference of your head into every common hat sizing system: US fitted sizes such as 7 1/4, UK sizes, European (centimetre) sizes and the S, M, L, XL letter sizes used for stretch-fit and flex caps. Enter your measurement in inches or centimetres and it does the conversion instantly.
Use it before ordering a fitted baseball cap, fedora, cowboy hat, beanie or cycling helmet online, or when buying a hat as a gift from a known measurement. The full size chart below the result shows neighbouring sizes so you can size up if you prefer a looser fit or plan to wear the hat over long hair.
To measure, wrap a soft tape around your head about 1/8 inch (3 mm) above your eyebrows and ears, across the widest part at the back. Keep it snug but not tight. Letter sizes vary a little between brands, so check the brand’s own chart when you are between sizes.
How to use the hat size calculator
- 1Wrap a soft tape measure around your head, just above the eyebrows and ears.
- 2Read the measurement where the tape meets, keeping it snug.
- 3Enter the number and choose centimetres or inches.
- 4Read your US, UK, European and letter sizes.
- 5If you are between sizes, go up one size for a comfortable fit.
Formula and method
US fitted hat sizes are based on the average diameter of the head: the circumference in inches divided by π, expressed in eighths of an inch. For example, a 22 3/4 inch head ÷ π ≈ 7.24, which is size 7 1/4. UK sizes run one eighth smaller than US sizes for the same head, and European sizes are simply the head circumference in centimetres, rounded to the nearest whole number.
Letter sizes group neighbouring fitted sizes: S covers 6 3/4–6 7/8, M 7–7 1/8, L 7 1/4–7 3/8, XL 7 1/2–7 5/8 and XXL 7 3/4–7 7/8. These are typical ranges; individual brands can differ.
- π
- Pi, about 3.1416
- circumference
- Distance around the head just above the ears and eyebrows
Worked examples
57 cm head
57 cm is 22.44 inches. Dividing by π gives 7.14, which rounds to 7 1/8 in US sizing. The UK equivalent is 7, European is 57 and the letter size is Medium.
22 3/4 inch head
22.75 ÷ π = 7.24, so the US size is 7 1/4 — a Large. That is 57.8 cm, European size 58, and UK size 7 1/8.
60 cm head
60 cm is 23.62 inches; ÷ π ≈ 7.52, which is a US 7 1/2. That corresponds to UK 7 3/8 and an XL in letter sizes.
Frequently asked questions
How do I measure my hat size?+
Wrap a flexible tape measure around your head about 1/8 inch above your eyebrows and ears, around the widest part of the back of your head. Use the measurement in inches or centimetres with this calculator.
What is the average hat size?+
Adult head circumferences commonly fall between about 55 and 59 cm, which is roughly US size 6 7/8 to 7 3/8. Size 7 1/4 (about 57.8 cm) is often cited as a typical men’s fitted cap size.
What size is 7 1/4 in cm?+
A US size 7 1/4 fits a head circumference of about 22 3/4 inches, or 57.8 cm. In European sizing that is size 58, and in letter sizes it is usually a Large.
Are UK and US hat sizes the same?+
No. UK hat sizes are one eighth smaller than US sizes for the same head, so a US 7 1/4 is a UK 7 1/8. European sizes use the head circumference in centimetres.
Should I size up if I am between hat sizes?+
Usually yes. A hat that is slightly big can be adjusted with sizing tape inside the band, but one that is too tight will be uncomfortable and can cause headaches.