[USFRIENDINVICTORIA]

The traditional or Imperial units were all based on practical applications -- metric tries to force everything into powers of ten. When Canada converted to metric, we had "soft" conversions for many things -- e.g. a pound of butter became 454 grams (close enough). Now, we buy butter in 500 gram packages -- in effect a "metric pound", although no one calls it that. A kilogram would be too big, a hectogram (100 grams) too small. Similarly, a gallon was a good size for a jug of milk -- 10 litres would be way too big. The metric system has had to adapt to the way people actually do things.

[Mr. Lucky]

Wasn't it always easier just to remember that: "a pint's a pound the world around"?

[-YYZ-]

It's the units that are powers of 10 of each other. No one ever expected that all common packages of everything would be an even unit. And the same is true in the old system - many drinks come in 12 oz servings - 12 oz is not an even measure of anything. 4 litres is a good size for a jug of milk, too, and neatly splits the difference between an US and an Imperial gallon.