Scale Weight Calculator — Cube Law Weight

Weight (mass) depends on volume, which is a three-dimensional quantity. If you shrink all three dimensions by the scale factor, volume shrinks by the scale factor cubed. A 1:72 model has 1/72 the length, 1/72 the width, and 1/72 the height, so its volume (and thus weight, assuming same density) is 1/(72x72x72) = 1/373,248th of the original.

No — this is the theoretical weight if the model were made of the same material as the real object. A real tank is made of steel, but a plastic model uses much lighter polystyrene. This calculation is mainly useful for understanding scale physics or for ballasting model railway wagons to realistic scale weights.

It tells you what a prototype wagon or loco would weigh at scale, which is a useful reference point. Note, though, that the recognised running-performance standard is NMRA RP-20.1, which is a fixed base weight plus a per-length amount, not a fraction of the cube-law scale weight. For HO that is 1 oz (28.3 g) plus 0.5 oz (14.2 g) per inch of car length; for N it is 0.5 oz plus 0.15 oz/in; for O it is 5 oz plus 1 oz/in. OO modellers typically follow the HO figures. The Ballast Target option here is only a rough convenience, not RP-20.1.