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Why are hat sizes so odd?

People come in all shapes and sizes. That’s reflected in the way that clothing is sized. For example, shirts may come in small, medium, large, and extra-large. Men’s pants are generally sold labeled with two numbers: one listing waist size, and the other length. Women’s dresses are a bit more amorphous with numbered sizes like 2, 6, 10…or even 0.

People are a lot of different sizes, but in spite of that, their heads really are not all that different. Nearly all adult heads have a circumference that sits somewhere within a five-inch range. That’s not a lot of variance, and why had sizes are so much more precise and specific, at least compared to a “size 4” dress or a “medium” shirt.

Hat sizes in the U.S. are listed by quarter inch. The smallest fitted size generally available for adults is a 6-3/4, and the largest is an 8. A “one size fits most” hat is usually around a 7-1/8 or 7-3/4. Every little bit matters in hat sizing, so that’s why hat sizes are so much more precise and specific, unlike a “size 4” dress or a “medium” shirt. But those actual sizes are not an actual, direct number, like the waist size listing on a pair of pants. It’s a number derived by measuring the circumference of a head to the nearest eighth of an inch, and then dividing by pi (the figure by which all circular measuring begins).

It makes a little more sense in Europe—hats there are sized by circumference in centimeters. (Except in France, which has a similar quirky hat sizing system that measures hats from 0 up to 9-1/2.)