Hat Size Calculator
Turn your head circumference into a US fitted hat size and the matching S/M/L/XL label.
Run a soft tape measure around your head about an inch above your ears and eyebrows, where a hat naturally sits. Keep it level and snug but not tight. The US fitted size is that circumference divided by pi, rounded to the nearest eighth.
Hat sizing varies by maker and by style — a stiff fitted cap runs truer than a stretchy beanie, and brands round differently. If you're between sizes, size up; a hat that's a touch loose beats one that pinches.
How it works
A fitted hat size is based on the diameter of your head, but the number you can actually measure is the circumference. The tool takes the distance around your head and divides by pi to get that diameter.
It then rounds the diameter to the nearest eighth of an inch, which is exactly how fitted hats are labeled — sizes like 7, 7 1/8, and 7 1/4. Alongside that, it gives the looser S/M/L/XL band that stretch-fit and adjustable hats use.
For reference, a head about 22.5 inches around works out to roughly a size 7 1/8 fitted hat, which sits in the medium range. Measure about an inch above your ears where the hat actually rests.
Frequently asked questions
How do I measure my head for a hat?
Wrap a soft tape measure around your head about an inch above your eyebrows and ears — where a hat sits — keeping it level and snug but not tight. Read the circumference in inches or centimeters.
What's the difference between fitted and S/M/L?
Fitted sizes like 7 1/4 are precise to the eighth-inch and don't stretch, so they only fit one head size. S/M/L/XL covers a range and suits adjustable or stretch-band hats that flex a bit.
Should I size up or down between sizes?
Size up. Hats stretch a little with wear, and a slightly loose hat is far more comfortable than one that leaves a mark. Beanies and knit styles are the most forgiving.