Mass Calculator guide
Mass Calculator: Find Mass From Density, Weight or Force
Use our mass calculator to find mass from density and volume, from weight and gravity, or from force and acceleration.
By the AllCalculator editorial teamUpdated 16 October 20261 min read
Mass is the amount of matter in an object. Our Mass Calculator finds it three ways.
How to use the calculator (Mass Calculator)
Choose how to work out the mass:
- Density and volume: m = ρ × V
- Weight (force): m = W ÷ g
- Force and acceleration: m = F ÷ a, from Newton's second law
Mass and weight
People often use the words interchangeably, but in science they're different:
- Mass is measured in kilograms and is the same everywhere.
- Weight is the force of gravity on that mass, measured in newtons. It's smaller on the Moon.
On Earth, weight = mass × 9.81.
A worked example
With the calculator's default settings, a steel block (density 7,850 kg/m³) with a volume of 0.01m³ has a mass of 7,850 × 0.01 = 78.5kg, or about 12st 5lb.
Frequently asked questions
Is the kilogram still defined by a metal cylinder?
Not since 2019. It's now defined using the Planck constant, a fixed number in physics.
What's Newton's second law?
Force = mass × acceleration (F = ma). A 2kg object accelerating at 3 m/s² needs a 6N force.
How do I convert stone to kg?
1 stone = 6.35kg. Our Unit Converter handles all weight units.
For an object's weight on other planets, see our Weight Calculator.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.