Mass Calculator

Density tells you how much mass is packed into each unit of volume, so multiplying it by a volume gives the total mass. The default example is one cubic meter of copper, whose density is about 8,900 kg/m³, giving a mass of 8,900 kilograms, or almost 20,000 pounds. The same approach tells you how much a load of gravel, a tank of water or a block of steel will weigh before you lift it.

What is mass?

Mass is a measure of how much matter an object contains and of how strongly it resists being accelerated, a property called inertia. Push a shopping cart and a loaded truck with the same force and the cart speeds up far more, because it has much less mass. Mass is also the source of gravitational attraction: every mass pulls on every other.

The SI unit of mass is the kilogram. From 1889 until 2019 it was defined by a platinum-iridium cylinder kept near Paris; it is now defined by fixing the value of the Planck constant, which lets any well-equipped laboratory realize it. A mass does not depend on where the object is. A 1 kg bag of flour has the same mass on Earth, on the Moon and floating in orbit.

For a uniform object, mass equals density multiplied by volume.

m = ρ × V

m

mass

ρ

density (rho)

V

volume

Convert density and volume to matching units first, e.g. kg/m³ and m³.

Mass vs. Weight

In physics, weight is a force: the pull of gravity on a mass. It is found by multiplying mass by the local gravitational acceleration, W = m × g, and is measured in newtons. On Earth, g averages about 9.81 m/s², so a 1 kg mass weighs about 9.81 N. Because g is almost the same everywhere on Earth's surface, scales can be calibrated to display mass directly, which is why people say they weigh 70 kilograms.

Off Earth the distinction becomes obvious. An astronaut's mass is unchanged on the Moon, but their weight there is about one-sixth of what it is on Earth, because the Moon's surface gravity is about 1.62 m/s². In orbit, astronauts are effectively weightless even though their mass, and therefore their inertia, is exactly the same; moving a heavy piece of equipment on the space station still takes effort.

Mass is measured with a balance, which compares an unknown mass with known ones and gives the same answer anywhere. A spring scale or bathroom scale measures force, so strictly it measures weight and would read low on the Moon. The table shows what a person with a mass of 70 kg would weigh elsewhere in the solar system.

Frequently asked questions