How much sand ?

I could be wrong but I thought the bags held 1 tonne?

Grit sand is the stuff used for floor screeds and is coarser than sharp sand. Your BM should have both

Bob

In message , Bob Minchin writes

Something like that, I suspect it is a nominal tonne, and that they are filled by volume in a BM. But yes it's probably more like 0.75m^3 for sharp sand. It varies of course by the density

It partly seems to be a regional thing. In Leeds they seemed to call sharp sand gritsand.

aAnyway for the OP's purpose I don't think it really matters.

Re compaction, the bed thickness is as laid. assuming we are talking concrete slabs here then it won't compact down That much anyway with laying - a few mm

I am fairly sure I use about 6 tons to lay 50 sq meters, admittedly at varying thickness up to 100mm.

I am fairly sre that a bag is 850kg roughly and is less than half a cubic meter.

Buy a ton bag delivered, and when you run out, buy another one.