Hat size converter
Convert hat sizes between US, UK, European, letter sizes and your head measurement in centimeters or inches.
That's about the same as an average man’s head. That fits a head of about 57.85 cm (22.78 inches) around.
What it means
Where does that size sit?
Measure around the head just above the ears and eyebrows. Between sizes, take the larger one; fitted caps run small.
Every unit
That hat in every system
Learn
Three things worth knowing
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US size × 8 ≈ cm
A 7⅛ hat is about 57 cm (7.125 × 8 = 57). It works within a centimeter across the adult range.
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Why divide by π
Hatters sized a hat by the diameter of the head it fits, as if heads were round. Circumference ÷ π gives that diameter in inches, and the eighths come from the hatter’s rule.
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UK and US sizes differ
A US 7¼ is a UK 7⅛. Buying a British hat in your US size gets you one an eighth too big.
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Popular hat size conversions
Background
About hat sizes
Every hat size starts with the circumference of your head. In Europe that number in centimeters is the size: a 57 fits a 57 cm head. US sizes divide the circumference in inches by π, so a 22.4-inch head is a 7⅛; UK sizes are an eighth smaller for the same hat.
Letter sizes cover two centimeters each: M is 57–58 cm, L is 59–60 cm.