How it works
Every unit converts through a base unit (meters, kilograms, liters, meters per second) using exact definitions: 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, and 1 US gallon = 3.785411784 liters.
Temperature uses formulas: °C = (°F − 32) × 5/9, and K = °C + 273.15.
Worked example
10 miles = 10 × 1,609.344 m = 16.09344 km. 100 °F = (100 − 32) × 5/9 = 37.78 °C. 150 lb = 68.04 kg.
Frequently asked questions
How many cm in an inch?
Exactly 2.54 centimeters.
How do I convert pounds to kilograms?
Multiply by 0.45359237, or divide by about 2.2046.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. 68 °F is 20 °C.
Are the volume units US or UK?
US customary. A UK gallon is larger, about 4.546 liters.