Metric or imperial? How the two systems fit together
One system counts in tens, the other in twelves, sixteens and fourteens. Here is how they line up.
Most of the world measures in metric units, while the United States still uses its customary units and the UK mixes the two. You do not need to pick a side. You only need to know how they connect.
Metric counts in tens
Every metric unit is built from a base unit and a prefix. Milli means a thousandth, centi a hundredth and kilo a thousand. So 1 kilometre is 1,000 metres and 1 metre is 100 centimetres. Moving between sizes is just a matter of moving the decimal point.
Imperial counts in everything else
- 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile
- 16 ounces in a pound, 14 pounds in a stone
- The US and UK gallons are different sizes: about 3.79 L and 4.55 L
The bridge between them
Since 1959 the inch has been defined as exactly 2.54 centimetres and the pound as exactly 0.45359237 kilograms. Every length and weight conversion on this site starts from those two exact numbers, so results never drift.
| Handy anchor | Approximately |
|---|---|
| 1 metre | 3.28 feet |
| 1 kilometre | 0.62 miles |
| 1 kilogram | 2.2 pounds |
| 1 litre | 1.06 US quarts |
Try it yourself