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A brief history
The metric system was introduced in France in 1795 and standardized internationally as the SI (Système International) in 1960. Imperial units descended from British customary measures and remain the official everyday system in the US, with limited use in the UK and a handful of other countries.
Key conversion factors
The most-used conversions in one place
| Quantity | Metric | Imperial | Factor |
|---|---|---|---|
| Length | 1 meter | 3.28084 feet | × 3.28084 |
| Length | 1 kilometer | 0.62137 miles | × 0.62137 |
| Weight | 1 kilogram | 2.20462 pounds | × 2.20462 |
| Volume | 1 liter | 0.26417 US gal | × 0.26417 |
| Volume | 1 milliliter | 0.0338 fl oz (US) | × 0.0338 |
| Temperature | 0 °C | 32 °F | × 9/5 + 32 |
Where each system is used
- Metric — used by every country except the US, Liberia and Myanmar for daily life; used universally for science, medicine and international trade.
- Imperial — official US system; common in UK road signs (miles), aviation worldwide (feet of altitude, knots) and consumer goods like TVs (inches).
Convert between them
Length conversion
Meter (m)
Foot (ft)
Press / to focus
| Unit | 1 m equals |
|---|---|
| Nanometer (nm) | 1.00000e+9 |
| Micrometer (µm) | 1.00000e+6 |
| Millimeter (mm) | 1,000 |
| Centimeter (cm) | 100 |
| Meter (m) | 1 |
| Kilometer (km) | 0.001 |
| Inch (in) | 39.3701 |
| Foot (ft) | 3.28084 |
| Yard (yd) | 1.09361 |
| Mile (mi) | 0.000621371 |
| Nautical Mile (nmi) | 0.000539957 |
Pitfalls to avoid
Gallons aren't gallons
A US gallon is 3.785 L; a UK (imperial) gallon is 4.546 L — about 20% larger. Always check which system a recipe or fuel-economy figure uses.
Area and volume scale non-linearly
1 ft = 0.3048 m, but 1 ft² = 0.0929 m² and 1 ft³ = 0.0283 m³. Square or cube the linear factor — never reuse it directly.
Related converters
The tools mentioned in this guide — one tap away.
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