How to use
Measure twice with your usual hairstyle. A string and ruler work if you do not have a soft tape. Do not measure a hat’s outside edge or use head width: this chart needs the complete circumference.
Choose centimeters or inches, enter your measured value and select Find my size. Decimal points and commas are accepted. Changing units converts your current measurement. Editing a value or changing a selection clears the confirmed Result and Copy state. Copy result includes the measurement, reference and interpretation. Clear removes your values; muted examples return when you leave an empty example field.
How to read the result
US fitted estimate = circumference in inches ÷ π, rounded to the nearest 1/8 (ties upward). The chart is generated from size × π × 2.54, not copied from a brand’s chart. Its cm values are rounded to two decimals. This is a starting point for fitting, not an exact specification for every hat. UK = US − 1/8.
Examples
57.7 cm → approximately US 7 1/4 / UK 7 1/8. 60 cm → approximately US 7 1/2 / UK 7 3/8. The nearest generated reference row is highlighted; its ideal circumference may differ from your measured value.
Questions about fit
Is this a manufacturer’s chart?
No. The reference is generated with the circumference/π relationship. It does not prescribe a brand’s size or fit.
What if I am between sizes?
The nearest eighth is shown as an estimate, not a promise that the smaller or larger hat fits. Head shape, hair and cap depth still matter.
Which countries does this cover?
US and UK fractions are shown separately. Metric sizing uses head circumference in centimeters, also used in Europe, Japan and Brazil. These are sizing conventions, not a universal fit guarantee.
Can I enter inches?
Yes, as a decimal. Selecting a different unit converts your measurement and clears the confirmed result; run the finder again.