Unit Converter
Convert length, mass, volume and temperature with named units and explicit conversion definitions.
Last updated: November 4, 2026
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Quick summary: Convert length, mass, volume and temperature with named units and explicit conversion definitions.
Read the complete guide
Updated reference sections in this guide are in English.
Choose the measurement before the units
Select length, mass, volume or temperature. The unit lists change together so that incompatible quantities cannot be mixed. Enter the measurement and choose its starting and destination units. Length uses the international foot and mile; mass uses the avoirdupois pound and ounce. Volume distinguishes a US liquid gallon from an imperial gallon.
Conversion through a base unit
Fahrenheit = Celsius × 9 ÷ 5 + 32
Kelvin = Celsius + 273.15
Length is converted through meters, mass through kilograms, and volume through liters. Temperature needs an offset as well as a scale factor, so it is handled separately. Negative Celsius and Fahrenheit values are allowed, but a result below absolute zero is rejected. Length, mass and volume fields represent nonnegative magnitudes.
Definitions used by this tool
| Unit | Definition used |
|---|---|
| 1 inch | 0.0254 meter |
| 1 international foot | 0.3048 meter |
| 1 international mile | 1609.344 meters |
| 1 avoirdupois pound | 0.45359237 kilogram |
| 1 US liquid gallon | 3.785411784 liters |
| 1 imperial gallon | 4.54609 liters |
These definitions determine the calculation rather than an approximate wallet-card factor. Browser arithmetic still has finite numerical precision; the interface formats the result instead of claiming unlimited significant figures.
Three conversion checks
Inches to centimeters
12 inches × 0.0254 meters per inch ÷ 0.01 meters per centimeter = 30.48 centimeters.
Two different gallons
10 US liquid gallons equal 37.85411784 liters. Ten imperial gallons equal 45.4609 liters. Selecting the wrong gallon can matter much more than display rounding.
Water-freezing reference
0 °C converts to 32 °F and 273.15 K. Temperature differences use scale factors without the same offset; this form converts actual temperature readings.
Check this scenario in the calculator:
- Measurement family
- Length
- Value
- 1
- From unit
- Meters
- To unit
- Feet
Precision and exclusions
A conversion does not make a measurement more accurate. Converting a roughly measured distance into twelve decimal places does not create twelve decimal places of measurement precision. This tool does not convert mass to volume, because that requires material density. Troy ounces, US survey feet, dry gallons, area and energy are not included.
Reference and questions
NIST SP 811, Appendix B.9: conversion factors by quantity provides reference factors and distinctions between unit definitions. The formulas and worked examples above explain this implementation.
Can I convert pounds to liters?
Not from units alone. Pounds measure mass and liters measure volume; a material-specific density is needed.
Does a negative Celsius value mean the input is invalid?
No. Negative Celsius values can be valid. The physical lower limit checked by this form is absolute zero, equivalent to 0 K.
What happens to very small results?
Small nonzero values are displayed in scientific notation when ordinary decimal formatting would hide them.