# Geometrized Unit¶

In general relativity, it’s quite useful to use geometrized unit, where everything has unit of kilometers. [Schutz]

The principle of geometrized unit is to convert everything to length using $$c=G=1$$. A precalculated value is

$1 = G/c^2 = 7.425\times 10^{-28}\mathrm{m} \mathrm{kg}^{-1}.$

In the spirit of this conversion, we have the mass of the Sun $$M_\odot=2.0\times 10^{30}\mathrm{kg} = 1.5\times 10^{3} \mathrm{m}$$ and mass of earth $$M_\oplus = 6.0\times 10^{24}\mathrm{kg} = 4.4 \times 10^{-3} \mathrm{m}$$.

## References and Notes¶

Schutz

A First Course in General Relativity (Second Edition)