Hat Size Calculator – Guide & Formulas
Determine your exact hat size in US, UK, EU (Metric), and Letter sizing systems based on your measured head circumference.
Try the free calculator
Put these formulas into practice with our instant, step-by-step Hat Size Calculator.
A well-fitting hat should rest comfortably without leaving deep marks on your forehead or feeling so loose that it slips off. This Hat Size Calculator converts your physical head circumference in inches or centimeters into standard fitted sizes for the US, UK, and European (metric) systems, as well as general letter sizes (S, M, L, XL).
Key Takeaway
Use the free Hat Size Calculator to determine your exact hat size in us, uk, eu (metric), and letter sizing systems based on your measured head circumference. Get instant results with step-by-step explanations.
How to Use the Hat Size Calculator
- Measure your head circumference using a soft tape measure.
- Enter your head circumference in either centimeters (cm) or inches.
- Review your calculated fitted sizes for US, UK, and European hat sizing systems.
- Check your corresponding standard letter size (Small, Medium, Large, etc.).
The Formula
Variable Definitions
- Head Circumference: The perimeter of the head measured about 1/8th inch above the ears
- \pi: Pi, the mathematical ratio of a circle's circumference to its diameter (~3.14159)
Determining Fitted Hat Size
A customer measures their head circumference and obtains a value of 23 inches (58.4 cm).
- Step 1: Set Head Circumference = 23 inches.
- Step 2: Apply the fitted formula: Fitted Size = 23 / 3.14159 ≈ 7.32 inches.
- Step 3: Round to the nearest standard fitted fractional size (e.g., 7 3/8).
- Step 4: This maps to an EU size of 59, UK size of 7 1/4, and a Letter size of Large (L).