About this hat sizes chart

How the data is built

Built from published conversion rules: the US fitted hat size is the head circumference in inches divided by pi, rounded to the nearest 1/8 inch; the UK size is the US size minus 1/8; the EU size is the head circumference in cm rounded to the nearest whole number. Letter (S-XXL) and stretch-fit bands are a general guide and vary by brand. All values hand-checked against multiple retailer charts on the date below.

The site's entire table — every number printed anywhere — lives in one checked data file, and every page is generated from it. Nothing on this site is hand-typed per page, which removes the class of copy-paste errors that make online hat charts disagree with each other.

What you can rely on

• The fitted table is exact. Adult heads from53.0 to 65.4 cm, in eighth-inch US steps, with UK, EU and letter sizes on every row.
• Letter and stretch-fit bands are a guide. Letter sizes vary by brand; check the brand's own chart.
• The converter is tested. A suite of test cases runs against the conversion code on every build.
• Last checked: 2026-10-21.