Definition:Metric System/Mass

Definition

Various metric units of mass which have specific names are as follows:

Milligram

$1$ milligram is defined as $= \dfrac 1 {1 \, 000}$ of a gram.

Gram

The gram is the CGS base unit of mass.

It is defined as the mass of a cubic centimetre water at the temperature of melting ice.

 $\ds$  $\ds 1$ gram $\ds$ $=$ $\ds 10^{-3}$ kilogram

Kilogram

The kilogram is the SI base unit of mass.

It is defined as follows:

$1$ kilogram is the quantity of mass that would make the fixed numerical value of the Planck constant $h$ to be $6 \cdotp 62607015 \times 10^{-34}$ when expressed in the unit Joule seconds.

The Joule second is equal to $1 \, \mathrm {kg} \, \mathrm m^2 \, \mathrm s^{−1}$, where the metre and the second are defined in terms of:

the speed of light $c$
the time of transition between the two hyperfine levels of the ground state of the caesium $133$ atom at rest at $0 \, \mathrm K$.
 $\ds$  $\ds 1$ kilogram $\ds$ $=$ $\ds 1000$ grams $\ds$ $\approx$ $\ds 2 \cdotp 20462$ pounds avoirdupois

Tonne

$1$ tonne is defined as $= 1000$ kilograms.
 $\ds$  $\ds 1$ tonne $\ds$ $=$ $\ds 1000$ kilogram $\ds$ $=$ $\ds 2204 \cdotp 62$ pounds avoirdupois $\ds$ $\approx$ $\ds 0 \cdotp 9842$ tons