Republic Standard Units

The (RSU) are more or less based on the metric system from the Earth-That-Was, however there are a few changes to accommodate space travel.

Earth-that-Was (ETWs)
An Earth-that-Was (often described as an ETW) is not so much a unit of measurement, rather a comparison.

It can be used to compare the radius (6,378.10 km = 1 ETW), land area of a planet (1.48 x 108 km2 = 1 ETW), mass (5.97 × 1024 kg = 1 ETW), density (5.52 g/cm3 = 1 ETW), gravity (9.81 m/s2 = 1 ETW), atmospheric pressure (101.33 kPa = 1 ETW), even orbital and rotational period (8,766 and 24 hours, respectively = 1 ETW).

Sol-that-Was (STWs)
In addition to ETWs for planets, STWs for stars are used.

It is primarily to measure radius (6.96 x 106 km = 1 STW), mass (1.99 x 1030 kg = 1 STW), and luminosity (3.85 × 1026 W = 1 STW).

Astronomical Units (AU)
The distance between a given planet and it's primary, or two stars in a multiple star system is measured in AUs. 1 AU is equivalent 1.50 x 108 km, or the distance between ETW and STW.

Light-years (ly)
The distance between stars outside of multiple star systems is measured in ly, the distance a photon would travel in one ETW year. 1 ly is equivalent to 63,241 AU.