From Rocket Scientist:
There are a bunch of good reasons to kiss the English system of measurement goodbye, not the least of which is that we’re the last damn country to be using it, including England. Here are a few of them.
*If math makes your eyes roll up into your head, skip to the end.
Units are ambiguous. You know a difference between a pound-force or a pound-mass? Most people don’t. So how much in an ounce? Troy, fluid, standard and, of course, there’s an ounce-force, too. How about a mile? There’s a survey mile, statute mile, Scottish mile, ancient English and Roman miles, Irish mile, international mile and no less that three different nautical miles. Note that the US uses no less than three of these forms of mile. Know how many different kilometers there are? Yep, just the one and they use the same damn one all over the world. The same liters, Newtons, kilograms… One and only one and everyone uses it, even us.
Different units for the same damn parameter. How many units do we have for distance? There’s, of course, all the different flavors of mile, foot and inch. Also furlong, mil, angstrom, parsec, league, yard… In metric there are meters and factors of 1000 of meters. That’s all. In volume, there are cubic inches and cubic feet, also gallons, pints, quarts, barrels, etc. In metric, there are liters and factors of 1000 of liters. The other side of the coin is that, by knowing the unit, you know the parameter. Newtons are force. Kg are mass. Pounds, of course, can be either. Ounces can be a measure of weight or a measure of force or a measure of volume.