Hat Size Calculator
Find your hat size from head circumference in US, UK, EU, and centimetre formats.
Formula
US hat size = circumference (in) ÷ π
- Measure head circumference 1 inch above the eyebrows at the widest point.
- US hat size ≈ circumference / π (diameter of a circle with that circumference).
- EU/CM sizes = head circumference in centimetres.
22.5-inch head circumference
Inputs
- Head Circumference: 22.5 in
22.5 in = 57.15 cm. US hat size = 22.5/π ≈ 7.16 → Size 7 1/8.
Frequently asked questions
How do I measure my head for a hat?
Use a flexible tape measure around the widest part of your head, about 1 inch above the eyebrows and ears.
What if I am between hat sizes?
Choose the larger size. Hat size reducers (foam strips inside the hat) can make a slightly large hat fit.
Are baseball caps sized differently?
Baseball caps use S/M/L or fitted (exact size). Use your US hat size for fitted caps.
What is an average hat size?
The average adult hat size is about 7 1/4 to 7 3/8 (US), corresponding to 22.5-23.5 inch circumference.