Metric to Imperial Conversion
Switching between the world's measurement system and America's: the factors, the history, and the shortcuts.
Converting metric to imperial means applying the exact defined factors: 1 kg = 2.20462 lb, 1 m = 3.28084 ft, 1 L = 0.264172 gal, 1 km = 0.621371 mi. The metric system is decimal and global; the US customary system descends from British imperial units and persists in American daily life.
The core factors
Weight: 1 kilogram = 2.20462 pounds; 1 gram = 0.035274 ounces. Length: 1 meter = 3.28084 feet; 1 centimeter = 0.393701 inches; 1 kilometer = 0.621371 miles. Volume: 1 liter = 0.264172 US gallons = 33.814 US fluid ounces. Temperature: C = (F - 32) x 5/9.
All of these derive from exact definitions (the inch is exactly 2.54 cm, the pound exactly 453.59237 g), so the conversions are exact to the decimals shown. Everyday rounding to 2-3 decimals is plenty.
Why the US still uses imperial
The US customary system descends from British imperial units, standardized in the 19th century. The Metric Conversion Act of 1975 made metric voluntary, not mandatory, and everyday life never switched: road signs, real estate, cooking, and body weight stayed imperial.
American industry is quietly bilingual: cars are engineered in metric, medicine doses in metric, the military uses metric (klicks for kilometers), while real estate, cooking, and weather stay imperial. Scientists and engineers worldwide, including in the US, work in metric.
Everyday shortcuts
Weight: kilograms to pounds, double and add 10 percent (70 kg -> 140 + 14 = 154 lb; actual 154.3). Pounds to kg, halve and subtract 10 percent of the half. Height: 180 cm is about 5 ft 11 in (divide cm by 2.54 for inches, then by 12).
Distance and speed: km to miles, multiply by 0.6. Liters to gallons, divide by 3.8. Milliliters to fluid ounces, divide by 30. These get within a percent or two, fine for travel and cooking, not for engineering.
Common mix-ups to avoid
The US gallon (3.785 L) is smaller than the imperial gallon (4.546 L) still used in the UK: a 'gallon' in a British recipe is 20 percent bigger. The US pint is 16 fluid ounces; the imperial pint is 20. Check which gallon a source means before converting fuel economy or recipes.
Tons differ too: the US short ton is 2,000 lb, the metric tonne is 1,000 kg (2,204.6 lb), and the British long ton is 2,240 lb. In international shipping, 'ton' almost always means the metric tonne.
Skip the arithmetic
Convert between the systems instantly with the free unit converter.
Metric/imperial questions
How do I convert kg to lbs?
Multiply kilograms by 2.20462. The quick mental version: double the kilograms and add 10 percent of the doubled number. 70 kg doubles to 140, plus 14, is 154 lb (actual 154.3).
Why does the US not use the metric system?
The Metric Conversion Act of 1975 encouraged but did not require metrication, so road signs, real estate, cooking, and weather stayed imperial. Meanwhile US science, medicine, manufacturing, and the military largely converted, leaving the country functionally bilingual in measurement.
Is a US gallon the same as a UK gallon?
No. The US gallon is 3.78541 liters while the British imperial gallon is 4.54609 liters, about 20 percent larger. The same split applies to pints and quarts. Always check which gallon a recipe, manual, or fuel-economy figure means before converting.