It seems that the US has their own special pint, called the US Liquid Pint, and contains a volume of 473 ml. (16 oz)
In the UK, the (Imperial) Pint is 20% bigger in volume (568 ml) at 20 oz.
I recall that in the days before we went metric and switched to litres for gasoline, our gallons were Imperial gallons and were bigger than the American gallon.
But anyways, the American pint is measured off as one eigth of a British Wine Gallon defined in 1707 as 231 cubic inches of volume.
In 1824, the Brits standardized their gallon to the Imperial Gallon size, which is the size of 10 pounds of distilled water at 62 degrees F. A british pint is one eigth of that.
In metric, a pint is usually rounded off to 500 mls.
Best of all I like the Scottish Pint: equal to 3 imperial pints. Too bad it is now obsolete!
http://en.wikipedia.org/wiki/Pint