What are the standard SI units for mass?

The standard SI unit for mass is the kilogram (kg).

The International System of Units, abbreviated as SI from the French "Système international", is the modern form of the metric system and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, one of which is the kilogram for mass.

The kilogram is defined as being equal to the mass of the International Prototype of the Kilogram (IPK), a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures in France. However, in 2019, the definition was revised to be based on fundamental constants of nature, specifically the Planck constant, to ensure its stability and universality.

In physics, mass is a fundamental property of matter. It is the measure of an object's resistance to acceleration when a net force is applied. It also determines the strength of its mutual gravitational attraction to other bodies. The unit of mass, the kilogram, is used in a wide range of measurements in physics, from calculating the weight of an object (where weight is the force of gravity acting on a mass) to determining the mass-energy equivalence in Einstein's famous equation E=mc^2.

It's important to note that while the kilogram is the base unit, other units such as the gram (g) and milligram (mg) are also used, particularly in contexts where smaller quantities are being measured. These are derived units, obtained by multiplying or dividing the base units. For example, 1 kilogram is equivalent to 1000 grams, and 1 gram is equivalent to 1000 milligrams.

In summary, the kilogram is the standard SI unit for mass, fundamental to many calculations and measurements in physics. Its definition, based on the Planck constant, ensures its stability and universality across different contexts and scales.