Hat Size Converter

The Hat Size Converter turns a single head measurement into every hat sizing system at once — US, UK, EU (metric), and international S–M–L letter sizes. Enter your head circumference in centimeters or inches, or start from a size you already own, and the tool shows your fitted size as an exact fraction, places you on a visual size gauge, and gives you a full conversion chart. Because every hat system is derived from the same circumference, the four answers always agree.

How to Measure Your Head for a Hat

An accurate hat size starts with an accurate measurement. You only need a soft tape measure (or a piece of string and a ruler):

1. Wrap the tape around the widest part of your head — about 1 cm (½ inch) above your ears and eyebrows, across the middle of your forehead.
2. Keep the tape level all the way around and snug but not tight — it should sit where the hat band will rest.
3. Read the number where the tape meets. Measure two or three times and use the largest reading for the best fit.
4. No tape measure? Wrap a string around your head, mark where it overlaps, then measure the string against a ruler.

Hat Size Formula

All four systems come from your head circumference. A US "fitted" size is simply the diameter of your head in inches:

For example, a head circumference of 22 inches (56 cm) gives 22 ÷ π ≈ 7.0, a US size 7. That equals a UK 6 7/8, an EU 56, and an international Small.

Hat Size Conversion Chart

This chart converts between US, UK, EU, and letter sizes across the common adult range. Head circumference is shown in both centimeters and inches.

US vs UK vs EU Hat Sizes

US and UK sizes both use the "fitted" system, where the number is the head's diameter in inches. The only difference is the reference point: a UK size runs exactly 1/8 inch smaller than the equivalent US size, so a US 7 1/4 is a UK 7 1/8. EU (European/metric) sizes throw out inches entirely and just use your head circumference in centimeters, which is why an EU size looks like a big number such as 57 or 59. Letter sizes (S, M, L, XL) are the most forgiving — each letter covers a small range of centimeters and is used mostly for stretch-fit and adjustable hats.

What If I'm Between Two Sizes?

Head measurements rarely land exactly on a size line. When you fall between two sizes, the rule is simple: size up. A hat that is a touch large can be tightened with its internal sweatband or a strip of hat-sizing foam tape, but a hat that is too small can never be made bigger. A well-fitting fitted hat sits snug all the way around, stays put when you tilt your head, and does not leave a red mark on your forehead.

Hat Fitting Tips

How to Use This Converter

1. Measure your head: Wrap a soft tape around the widest part of your head, about 1 cm above your ears and eyebrows.
2. Enter the measurement: Choose centimeters or inches and type your circumference, or switch to "a size I already know" and pick it from the list.
3. Click Convert: The tool instantly shows your US, UK, EU, and international sizes.
4. Review the results: Check the animated tape diagram, the size gauge, your fitted-size fraction, and the highlighted row in the full conversion chart.

Frequently Asked Questions

How do I measure my head for a hat?

Wrap a soft cloth tape measure around the widest part of your head, roughly 1 centimeter (about half an inch) above your ears and eyebrows. Keep the tape level and snug but not tight. The number where the tape meets is your head circumference, which you can enter in centimeters or inches.

How is a US hat size calculated?

A US fitted hat size is the diameter of your head in inches, which equals your head circumference in inches divided by π (about 3.1416), rounded to the nearest one-eighth inch. For example, a 22 inch circumference divided by π is about 7.0, which is a US size 7.

What is the difference between US and UK hat sizes?

UK hat sizes use the same fitted-size system as US sizes but run exactly one-eighth of an inch smaller. So a US 7 1/4 is a UK 7 1/8, and a US 7 is a UK 6 7/8.

What is my EU hat size?

European (metric) hat sizes are simply your head circumference in centimeters, rounded to the nearest whole number. A 57 cm head is an EU size 57, which corresponds to a US 7 1/8 and an international Medium.

What if my head is between two sizes?

If your measurement falls between two sizes, size up. A slightly larger hat can be tightened with the internal sweatband or a strip of hat-sizing foam tape, whereas a hat that is too small cannot be made bigger. Fitted hats should feel snug all the way around without leaving a mark.

Are hat sizes the same for men and women?

The measurement and conversion math are identical for everyone, because hat sizing is based purely on head circumference, not gender. Average adult men measure about 57 to 59 cm and average adult women about 55 to 57 cm, but you should always use your own measured circumference rather than a gender assumption.

Additional Resources

• Hat - Wikipedia
• Circumference - Wikipedia