# International System of Units

Links between the seven SI base unit definitions. Clockwise from top: kelvin (temperature), second (time), metre (length), kilogram (mass), candela (luminous intensity), mole (amount of substance) and ampere (electric current).

International System of Units – the standard modern form of the metric system. The name of this system can be shortened or abbreviated to SI Units, from the French name Système International d’unités.

The International System of Units is a system of measurement based on 7 base units. These base units can be used in combination with each other. This creates SI derived units, which can be used to describe other quantities, such as volume, energy, pressure, and velocity.

• the metre (length), kilogram (mass)
• second (time)
• ampere (electric current)
• Kelvin (temperature)
• mole (quantity)
• candela (brightness)

Planck constant links the amount of energy a photon carries with the frequency of its electromagnetic wave. It is named after the physicist Max Planck. It is an important quantity in quantum physics. The Planck constant is defined by the equation:

• E = h\nu.

In SI Units the Planck constant is about 6.62606×10−34 J·s.[1] Scientists have used this quantity to calculate measurements like the Planck length and the Planck time.