The density of sand depends very much on the moisture content and how packed it is. At the SImetric in he UK you can find densities in kilograms per cubic meter. You can get Google to do the conversion. For example suppose you have wet sand with the density of 1922 kilograms per cubic meter. Got to Google and type 1922 kilograms per cubic meter to pounds per cubic foot into the search window. Google will respond with (1 922 kilograms) per (cubic meter) = 119.98654 pounds per (cubic foot). Since you have half a cubic foot the weight would be 60 pounds.

I hope this helps
Penny