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