SI base units

The SI base units are measurements used by scientists and other people around the world.

These SI base units and their physical quantities are:

This fact allows one to express the power-to-weight ratio purely by SI base units.

There are seven SI base units.

The first of these classes are the seven SI base units for length, mass, time, temperature, electric current, luminous intensity and amount of substance.

There are a number of proposals to redefine certain of the SI base units in terms of fundamental physical constants.

As a derived unit it is composed from the SI base units of length, the metre, and the standard unit of time, the second.

In slightly more fundamental terms, 1 joule is equal to 1 newton-metre and, in terms of SI base units:

The standard data file uses the SI base units as its fundamental units of measure, and extends this with units for currency and information (bits).

Expressing a CGS derived unit in terms of the SI base units, or vice versa, requires combining the scale factors that relate the two systems:

The pascal can be expressed using SI derived units, or alternatively solely SI base units, as:

These changes will have the effect of redefining the SI base units, though the definitions of the derived SI units will remain the same.

The 7 SI base units are used to define all other SI units, which are known as SI derived units.

Like other SI base units, the candela has an operational definition-it is defined by the description of a physical process that will produce one candela of luminous intensity.

The kilogram is inconsistent with the other SI base units in that it is expressed as a multiple of another unit (the gram) with a multiplier prefix ("kilo") added to it.

The SI unit of weight is the same as that of force: the newton (N) - a derived unit which can also be expressed in SI base units as kg m/s (kilograms times meters per second squared).