Definition:Metric System/Mass

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


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


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


$1$ 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