Unit Conversion Formulas
The idea behind most conversions
Most unit conversions multiply by a fixed factor. If one inch is 2.54 centimeters, then inches to centimeters is inches * 2.54, and centimeters to inches is centimeters / 2.54.
Common length and weight formulas
These are the conversions people reach for most often when working across metric and imperial systems:
- inches to centimeters:
in * 2.54 - feet to meters:
ft * 0.3048 - miles to kilometers:
mi * 1.609344 - pounds to kilograms:
lb * 0.45359237 - ounces to grams:
oz * 28.349523125
Temperature is different
Temperature uses an offset as well as a scale. Celsius to Fahrenheit is (C * 9 / 5) + 32. Fahrenheit to Celsius is (F - 32) * 5 / 9. Kelvin starts from absolute zero, so K = C + 273.15.
Speed conversions
Speed works like length divided by time. Kilometers per hour to miles per hour is km/h * 0.621371. Miles per hour to kilometers per hour is mph * 1.609344.
Use the converter
Open the Unit Converter, choose length, weight, temperature or speed, then enter a value to get the converted result instantly.
Try the Unit Converter →Convert between units of length, weight, temperature and speed. Free online unit converter with instant results. Metric ↔ Imperial.Frequently asked questions
Why are some conversions exact and others rounded?
Some definitions are exact, such as 1 inch = 2.54 centimeters. Displayed results may still be rounded for readability.
Why can I not multiply Celsius by one factor?
Because Celsius and Fahrenheit use different zero points. You need both multiplication and addition or subtraction.
Is metric easier for conversions?
Usually, yes. Metric units scale by powers of ten, while imperial conversions often use separate factors.