I apologize if there's already another thread like this, but the word "size" appears too frequently in this forum for the search feature to be of much use. Anyhow, the other day, I was pondering the U.S. hat sizing system, and wondering why it was the way it was. The numbers themselves don't seem to be connected to the width or length of the interior, nor do they represent the circumference; thus, they seem quite unintuitive compared to the European "circumference in centimeters" system. I'm not familiar with the history of how hat sizes came to be, so I'm basically completely in the dark. Long story short, I started playing with numbers, and eventually, I stumbled on to an interesting finding: If you multiply the US hat size by pi, you get almost exactly (at least, close enough for me) the circumference of the sweatband in inches. Take my size, 7 ¼. Multiply that by pi, and you get: 7.25 * π = 22.777 It's rounded off to the nearest thousandth, but you get the idea: it's a hair over 22 ¾". Now, let's convert that to centimeters: 22.777 * 2.54 = 57.854 That's right... just under a millimeter and a half away from the metric size. Now, obviously, the use of pi seems a little strange: hats are not completely circular, nor are the heads they sit on. But, it makes sense when you consider that, for the same circumference, hatters would produce different "ovals" with different degrees of eccentricity. In order to give them uniform size, it makes sense to consider them in terms of a circle, even though people's heads are not: dividing by pi gives you the diameter of that hypothetical circle, which will be the same regardless of the "oval-ness" of the finished hat. In so doing, I believe that the basis of U.S. hat sizes can be expressed as the following: U.S. hat size is equivalent to the diameter, expressed in inches, of a circle with the same circumference as the head of the intended wearer. Looking at it this way, one wonders how the metric sizing got to be the way it is, but my thinking is that they extrapolated from the increments of the U.S. or U.K. system to just write the circumference in centimeters, rounding to the nearest whole number for the sake of convenience. It is interesting how the U.S. sizing increments just so happen to be about (not quite exactly) a centimeter apart, though. An interesting coincidence? That said, I can't help but wonder about U.K. hat sizes now. They obviously ought to have the same origin as the U.S. system, since they're simply shifted over by ⅛, but they make less intuitive sense when viewed through this lens... [huh]

Perhaps the UK system is supposed to be based on the size of the head the hat would fit on rather then the hat itself? I've wondered about that one in the past as well. Never really pondered it that seriously though.

Did you know that you can measure the speed of light if you know your hat size? http://njsas.org/projects/speed_of_light/02/exp3.htm