Whether you're fond of fedoras, beguiled by berets, smitten with Stetsons or pretty in a picture hat, you'll want a perfect fit for comfort and your best look. America's favorite, the baseball cap, uses the same sizing system, too. It's easy to find your size.
Find a flexible measuring tape – the cloth kind, not a metal one that won't bend easily. Wrap the tape around your head, ear to ear. In the front, it should be across your temples and above your eyebrows. In the back, the tape should be across the occipital bone – the bump in the middle of your head. If you don't have a measuring tape, you can use a piece of yarn or string, and then measure it against a ruler. It won't be quite as accurate, though.
Consult a sizing chart. American sizing is in inches, starting with the smallest size, usually 6, at about 18.7 inches, to size 8, which measures 25 inches. Some hats are labeled from Extra Small to 3X Large instead of numerically. If you can't find a hat in your size, round up to the nearest 1/4 inch. If you have a vintage hat or one from a European maker, consult a size chart with an international measurement conversion. English sizes begin at 5 7/8 – an American 6 – and the French equivalent to this size is 1/2.
Try the hat on and adjust for comfort. It should be comfortable but not tight. On the other hand, you don't want it flying off or sinking over your eyes. You can pad with felt bands under the sweatband; ladies can also anchor the hat with a hatpin or bobby pins.