Hat Size Converter
Convert head circumference to US, UK, and EU hat sizes in inches and centimeters.
Includes a full hat size chart and measuring instructions for an accurate fit.
Hat size is based on head circumference — the measurement around the widest part of your skull. Hat sizing systems differ between countries, so understanding the conversion is essential when shopping internationally.
The Measurement Formula:
Hat size (US) = Head circumference (inches) / π ≈ Head circumference (inches) / 3.14159
Or: Head circumference (cm) / 3.14159 = hat size in cm (European style)
Measurement Technique:
Wrap a soft tape measure around the head approximately 2.5 cm (1 inch) above the eyebrows and ears, at the widest point. Do not pull tight — a natural fit.
Hat Size Conversion Chart:
| Head Circumference | US Size | UK Size | EU (cm) |
|---|---|---|---|
| 53–54 cm (21–21.25 in) | 6⅝ | 6⅝ | 53–54 |
| 55–56 cm (21.5–22 in) | 6¾–6⅞ | 6¾–6⅞ | 55–56 |
| 57–58 cm (22.5–22.75 in) | 7–7⅛ | 7–7⅛ | 57–58 |
| 59–60 cm (23.25–23.5 in) | 7¼–7⅜ | 7¼–7⅜ | 59–60 |
| 61–62 cm (24–24.5 in) | 7½–7⅝ | 7½–7⅝ | 61–62 |
| 63–64 cm (24.75–25.25 in) | 7¾–7⅞ | 7¾–7⅞ | 63–64 |
Worked Example:
Head circumference = 58 cm.
US hat size = 58 / 3.14159 = 18.46 cm diameter Traditional US hat size ≈ 7⅛ (reading from the circumference column)
Hat Fit Tips:
| Issue | Solution |
|---|---|
| Hat too loose | Use hat sizing tape inside the sweatband |
| Hat too tight | Steam and gently stretch over a wooden block |
| Oval head (longer front-to-back) | Look for “oval” or “long oval” shaped hats |
Practical Tips:
- Measure head circumference twice and take the larger of the two measurements
- Head size changes slightly through the day — measure in the afternoon when it’s at its largest
- Wool felt hats stretch 1–2 sizes after wear; buy fitted or slightly firm
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.