Quantity of matter of an object.

  • Mass is the property of an object to be more or less heavy.
  • The mass of an object only depends on its volume and the materials that form the object.
  • The mass of an object does not vary based on the location in the universe where we measure it.
  • On the other hand, the weight of an object depends on where it is (on Earth or on the Moon, at the North Pole or the Equator, etc.). The weight of a body is a force, mainly due to the action being exerted on it by Earth’s gravitational field.


The unit of measure of mass in the International System is kilogram. For large quantities, we use the metric tonne, which is equal to 1000 kilograms. Before the kilogram, there were traditional units like the pound, that was worth approximately slightly less than a half-kilogram, but whose value can vary depending on the region.

The main units of measure of mass are:

  • 1 t = 1000 kg which is read as “1 metric tonne” is equivalent to 1000 kilograms.
  • 1 kg = 1000 g which is read as “1 kilogram” is equivalent to 1000 grams.
  • 1 g = 1000 mg which is read as “1 gram” is equivalent to 1000 milligrams.


  • The mass of the Earth is about 6 000 000 000 000 000 000 000 kg.
  • The mass of a car is about 1450 kg.
  • The mass of an adult man is about 80 kg.
  • The mass of a pill is about 1 g.

Historical Note

The tonne is not a SI unit, but its use is associated with the SI because of its significant practical role.
One cubic metre of water weighs one tonne.

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