How to use the mass calculator
- Choose how to find the mass: density × volume, or weight ÷ gravity.
- For density × volume, enter the density (kg/m³, g/cm³ or lb/ft³) and the volume (m³, L, cm³, ft³, in³ or US gallons).
- For weight ÷ gravity, enter the weight as a force in newtons, pound-force or kilogram-force, and choose where it was measured: Earth, the Moon, Mars, Jupiter or a custom gravity.
- Choose the unit to show the mass in. The results list it in every common unit, with the working.
How mass is calculated
Mass is the amount of matter in an object, measured in kilograms. Weight is the force that gravity exerts on that mass, measured in newtons. Standard gravity, 9.80665 m/s², is the exact value adopted by the General Conference on Weights and Measures in 1901 and used by NIST to define the pound-force and kilogram-force. The Moon, Mars and Jupiter values come from the NASA Planetary Fact Sheet.
Worked example
The defaults are 1,000 cm³ of steel at a density of 7.85 g/cm³:
- Density in SI units: 7.85 g/cm³ = 7,850 kg/m³
- Volume in SI units: 1,000 cm³ = 0.001 m³
- Mass: 7,850 × 0.001 = 7.85 kg
- In pounds: 7.85 ÷ 0.45359237 = 17.31 lb
- Its weight on Earth: 7.85 × 9.80665 = 76.98 N (17.31 lbf)
Switch to weight ÷ gravity. A force of 700 N measured on Earth gives 700 ÷ 9.80665 = 71.38 kg (157.4 lb). A weight of 150 lbf gives 150 × 4.44822 ÷ 9.80665 = 68.04 kg, which is exactly 150 lb, because the pound-force is defined with standard gravity.
Mass vs. weight
| Mass | Weight | |
|---|---|---|
| What it is | Amount of matter | Force of gravity on that matter |
| SI unit | kilogram (kg) | newton (N) |
| US unit | pound (lb), slug | pound-force (lbf) |
| On the Moon | Unchanged | About 16% of Earth's |
| Measured with | Balance scale | Spring or electronic scale |
In everyday language "weight" usually means mass, and a bathroom scale displays kilograms or pounds by assuming Earth's gravity. Take the same scale to the Moon and it would show about a sixth of the number, though your mass hasn't changed. In engineering, keep the two apart: a 1 kg mass weighs 9.81 N, and confusing them is a common source of errors in force calculations. To find weight on other planets, use the weight calculator.
Mass units
| Unit | In kilograms |
|---|---|
| Gram (g) | 0.001 |
| Ounce (oz) | 0.028349523 |
| Pound (lb) | 0.45359237 |
| Slug | 14.593903 |
| US short ton | 907.18474 |
| Metric ton (t) | 1,000 |
The slug is the US customary unit of mass that accelerates at 1 ft/s² under a force of 1 lbf. It turns up in physics and aerospace work that uses feet and pounds-force. To find a volume or density instead of a mass, use the density calculator.
Frequently asked questions
Is mass the same everywhere?
Yes. Mass depends only on how much matter there is, so 70 kg on Earth is 70 kg on the Moon. Your weight there would be about 112 N instead of 686 N, because the Moon's gravity is weaker.
How do I convert newtons to kilograms?
Divide by the gravitational acceleration. On Earth, 1 kg weighs 9.80665 N, so 100 N corresponds to a mass of 100 ÷ 9.80665 = 10.2 kg. This only holds where g is known.
What is the difference between a pound and a pound-force?
A pound (lb) is a unit of mass, 0.45359237 kg. A pound-force (lbf) is the weight of one pound under standard gravity, 4.448 N. On Earth the numbers match, which is why people use "pounds" for both.
How do I find mass from density and volume?
Multiply them in matching units: kilograms per cubic meter times cubic meters, or grams per cubic centimeter times cubic centimeters. A liter of water at 1 g/cm³ (1,000 cm³) has a mass of 1,000 g.
Related calculators
- Density Calculator — Solve ρ = m ÷ V for density, mass or volume in metric or US units, with common material densities.
- Weight Calculator — Weight force W = m × g on Earth, the Moon and the planets, in newtons, pound-force and kilogram-force.
- Molarity Calculator — Molarity from mass and volume, the mass of solute to weigh out, the volume needed, and C₁V₁ = C₂V₂ dilutions.
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