Try some on until you find one you like. . . .

Go to a hat shop (Lids/Hat World) and try on some caps. Or you can get one of those little measuring tapes and wrap it around your cranium.

You measure around the head. At the point above your eyebrows and around the the back of your head. Try them on first. Some people like the looser than others.

Just go to a sporting goods store and try on a bunch of hats and then see which one fits the best then look at the size. I think that you can measure around your head and see what it is in inches

Ill give you a link for a chart.

Probably the same way as for a football helmet-but keep the hair at the same length, or the fit will fail.

Make sure your head isn't going to grow any larger (ya know, no HGH or cream or clear), visit a lid shop...choose your lid...take into account your hair style, the length/thickness of your hair will affect the fit...the new pro style caps shouldn't shrink if you sweat in them or let them get wet in the rain.