Many equations in relativistic physics appear simpler when expressed in geometric units, because all occurrences of G and of c drop out.
For this reason, many books and papers on relativistic physics use geometric units.
An alternative system of geometrized units is often used in particle physics and cosmology, in which 8πG = 1 instead.
Geometrized units were defined in the book Gravitation by Charles W. Misner, Kip S. Thorne, and John Archibald Wheeler with the speed of light,
This is dimensionally consistent with the notion that, according to the kinematical laws of special relativity, time and distance are on an equal footing.
For example, the Sun's mass of 2.0×1030 kg in SI units is equivalent to 1.5 km.
The small numerical size of the few conversion factors reflects the fact that relativistic effects are only noticeable when large masses or high speeds are considered.