Originally Posted by Hedgehog

The English system is much easier for approximations because its core measurements are based on amounts that are useful for everyday life.

A Gallon is the amount of water a person should drink a day, whereas a liter ain't enough. An ounce is about a mouthful, and a milliliter is but a drop on the tongue. A quart is a quarter of a gallon (duh?), and is the perfect amount of milk to buy and drink before it goes sour. A pint is the perfect size for a beer, whereas a liter would lose its head before you could finish it. A foot is about (duh!) the length of a male's foot and a yard is your average pace (2 steps), thus you can estimate the length of something much easier than in meters. A pound is the weight at which you have to strain slightly to hold it in your outstretched hand, whereas a gram can be blown away by a slight breeze.

The metric system just isn't convenient for everyday measures. The US uses metrics for everything that requires precise measurements, though.