Weight and Mass Converter
Convert between mass and weight units: kilograms, grams, pounds, ounces, stones, tonnes, and newtons. Explains the difference between mass and weight and shows the physics formula W = m × g.
Full original guide (expanded)
Weight and Mass Converter
Convert between common mass units (kg, g, lb, oz, stone, tonne) and weight/force units (N, kN). Choose your input unit and get all the others instantly.
Enter the number to convert.
Force units will be converted to the equivalent mass on Earth.
Highlights
Using standard gravity g = 9.80665 m/s² for weight.
Mass units
Weight / Force
Physics behind it
weight (N) = mass (kg) × g
g = 9.80665 m/s² (standard)
mass (kg) = weight (N) ÷ g
1 lb = 0.45359237 kg, 1 oz = 0.028349523125 kg, 1 stone = 6.35029318 kg
On the Moon or Mars the same mass would have a smaller weight because g is smaller. This calculator uses standard Earth gravity, which is what most tables and engineering problems assume unless stated otherwise.
Common conversions
| kg | lb | N (on Earth) | oz |
|---|
Values rounded. For precise metrology, use exact constants.
Mass vs weight: the short version
Mass is “how much stuff” something has. It does not change if you go to the Moon. It is measured in kilograms (kg).
Weight is the pulling force of gravity on that mass. On the Moon you weigh less, because gravity is weaker. Weight is measured in newtons (N).
Why do people say “I weigh 70 kg”?
That’s common language. Scales on Earth are calibrated so that the force of gravity is translated straight into kg. Behind the scenes, the scale assumes Earth gravity and converts N → kg.
When to use which
- Physics / engineering → use kg for mass, N for weight.
- Cooking / everyday → grams, kilograms, ounces, pounds.
- International / SI → prefer kg for mass, N for weight.
FAQ
1. Why is my kg ↔ N different from a textbook?
Some textbooks use g = 9.81 m/s². We used 9.80665 m/s² (standard gravity). Difference is tiny.
2. Can I convert kN to tonnes?
Yes: kN → N → kg → t. This tool already does that chain for you.
Formula (LaTeX) + variables + units
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weight (N) = mass (kg) × g g = 9.80665 m/s² (standard) mass (kg) = weight (N) ÷ g 1 lb = 0.45359237 kg, 1 oz = 0.028349523125 kg, 1 stone = 6.35029318 kg
- No variables provided in audit spec.
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.