Various Densities of Sandpaddler of the Precious Metal board posted this nice bit of info.
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The variance in weight of a cubic meter of sand/gravel/wet/ dry can be quite substantial. These figures are for KG/cu meter:
and sand alone can vary dramatically:
You would think the company, for its own information and planning would pick another method.
source:
https://www.simetric.co.uk/si_materials.htm