Unit
Unit Symbol
Base Measure
Physical Constant
Definition
Kilogram
kg
Mass
Plancks Constant (h) - relationship between a photons energy and frequency
Defined by taking Plancks constant (h) to be a fixed numerical value of 6.62607015×10−34 m2⋅kg⋅s–1
- Until 2019 the kilogram was defined as “the mass equal to the International Prototype of the Kilogram (IPK), a platinum-iridium rod housed at the International Bureau of Weights and Measures in Sevres, France”
- This was changed to create a definition based on a physical constant in line with the other base SI units