Hat Size Converter

In short A US hat size is the diameter of your head in inches. That is the entire definition, and it is why hat sizes are strange numbers between 6 and 8 rather than anything resembling a circumference: 7¼ means a head 7¼ inches across. Since a head is close enough to a circle, the size is the circumference divided by π, rounded to the nearest eighth — so a 58 cm head is 22.83 inches around, 22.83 ÷ 3.14159 is 7.27, and the nearest eighth is 7¼. Work that division through every row of any published hat chart and it reproduces the whole thing exactly, from 54 cm to 64 cm, which tells you the chart was never anything but this formula written out. The UK ladder is the same one shifted an eighth smaller, so the same head is a UK 7⅛ — a difference of one eighth, consistently, at every size. The European number needs no conversion at all: it is simply the circumference in whole centimetres, which is why a European hat says 58 and an American one says 7¼ for the same hat. To measure, put a tape around the widest part of your head — just above the ears and across the middle of the forehead — snug but not tight, and take the larger reading if you are between two. A hat that is slightly large can be brought in with sizing tape inside the band, and a hat that is slightly small can never be let out.