Mass converter
Convert mass between metric and imperial units.
Fill in the fields and the result will appear here automatically.
Converts mass between milligrams, grams, kilograms, tonnes, ounces, pounds and stones. Unit factors are exactly defined; calculation and result display have finite precision.
How it works
Formula and logic
Every unit has an exact factor to the kilogram, and conversion goes through that base.
Example
A pound is exactly 453.59237 grams and a stone is fourteen pounds.
Fields and units
- Mass — in the selected source unit
- From unit — list option
- To unit — list option
How to use
- — Enter the value.
- — Pick the source unit.
- — Pick the target unit.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- BIPM: SI Brochure, version 4.01 (2026) NIST: conversion-factor tables, Appendix B.9
- Limitation
- The result is a rounded unit conversion. Check the entered value and selected units.
FAQ
Is the pound conversion exact?
The avoirdupois pound is exactly defined: 1 lb = 0.45359237 kg. Finite-precision arithmetic and display rounding can still reduce the digits shown.
How is an ounce different from a troy ounce?
This converter uses the avoirdupois ounce used in trade. The troy ounce for precious metals is heavier and is not included.
What is a stone?
A British unit of 14 pounds, about 6.35 kg. It is still used for body weight in the UK and Ireland.
Are mass and weight the same?
In everyday use yes, but strictly weight depends on gravity. This converter works with mass.