Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A kilogram (kg) is the base unit of mass in the International System of Units (SI). It is defined by the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder stored in France.
5 Must Know Facts For Your Next Test
The kilogram is the only SI base unit that includes a prefix.
It was originally defined in 1795 as the mass of one liter of water at its freezing point.
In 2019, its definition was redefined based on physical constants, specifically Planck's constant.
1 kilogram equals 1000 grams.
Kilograms are commonly used in scientific measurements and everyday life to measure weight and mass.
Review Questions
Related terms
Gram (g): A metric unit of mass equal to one thousandth of a kilogram.
Planck's Constant: $h$ is a fundamental constant used to redefine the kilogram, with a value approximately equal to $6.626 \times 10^{-34} \text{Js}$.
International System of Units (SI): A globally accepted system for measurements based on seven base units including meter, kilogram, second, ampere, kelvin, mole, and candela.