Subscribe to download
Simple Properties Setter

Allows you to precisely set the mass and scale of an object via the context menu settings.
The conversion from arbitrary units(n) to actual mass in kg is n * 40.
Values may be prone to floating point math errors, making the values end in a recurring decimal (usually .99999).

"Scaled mass" in the set mass setting means the actual mass of the object after applying scaling math to it (since objects get heavier as you resize them).

Mass and size will be saved regardless of whether the mod is installed or not (you don't need to download this for any contraption to work).