How it works
Length, weight and volume units are converted through one base unit per category — meters, kilograms and liters. Each unit has an exact factor to its base unit, so a conversion is one multiplication and one division:
result = value × factor of the “from” unit ÷ factor of the “to” unit
The factors are the exact international definitions, for example:
| Unit | Exact definition |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 0.3048 m |
| 1 mile | 1,609.344 m |
| 1 pound | 0.45359237 kg |
| 1 troy ounce | 31.1034768 g |
| 1 US gallon | 3.785411784 L |
Temperature is different, because the scales don’t start at the same zero. The calculator converts through kelvin:
Example
- 10 feet to meters: 10 × 0.3048 = 3.048 m
- 5 US gallons to liters: 5 × 3.785411784 = 18.92705892 L
- 68 °F to Celsius: (68 − 32) × 5 ÷ 9 = 20 °C
Notes and assumptions
- US and imperial units differ. A US gallon is about 3.785 L, an imperial (UK) gallon 4.546 L. US cups, pints and quarts are also smaller than their imperial counterparts. Units marked “US” use US customary definitions.
- Weight means mass here. Pounds and kilograms are units of mass; the converter does not depend on gravity.
- Troy ounces (for gold and other precious metals) are heavier than ordinary ounces: 31.10 g versus 28.35 g.
- Results are calculated with exact decimals and rounded only for display. Temperatures below absolute zero (−273.15 °C) are rejected because they can’t exist.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54. Since 1959 the inch has been defined as 2.54 centimeters.
Is a US cup the same as a metric cup?
No. A US customary cup is about 236.6 ml, while recipes from many other countries use a 250 ml metric cup.
Why does the converter use kelvin for temperatures?
Kelvin starts at absolute zero, so every temperature can be converted to it and back without special cases. It also lets the calculator detect impossible values below absolute zero.
Which units are exact?
All length, weight and volume factors in this converter are exact by definition. Rounding only happens when a result has more digits than the display shows.