Inches and centimetres appear in the same document. Where each is used.
In the metric system every unit connects by powers of ten, so conversion is a matter of moving the decimal point. Imperial multipliers vary: twelve inches to a foot, three feet to a yard, sixteen ounces to a pound, all of which must be memorised. In exchange, common everyday sizes land on numbers that divide conveniently.
Most countries use the metric system, yet imperial units persist in specific fields because industry standards settled that way.
A gallon differs in value by region, and so does an ounce. Converting a figure from foreign material by unit name alone therefore goes wrong. Confirming which region's definition applies matters more than memorising the formula.
An ounce measures weight in one usage and volume in another. The shared name causes confusion, but they measure different things and their relationship depends on the substance. Confusing the two in a recipe changes the result considerably.
Units such as pyeong, geun, don and gwan remain in use. Property area is officially in square metres but often spoken in pyeong, gold trades in don and meat in geun. These have defined values and can be converted, though conventions vary by region and by item.
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