Answer: The weight of soils vary considerably. Clay soils are heavier than sandy ones, and moist ones are heavier than dry ones. But typical soils weigh about 100 pounds per cubic foot. So your calculation is pretty easy if you're considering an average topsoil: You'll need about 100 tons.
But in our experience, bulk materials are more often sold by the cubic yard. You might want to double check with your suppliers. In other words, they may charge by the ton but measure by the cubic yard.
There are 27 cubic feet in one cubic yard meaning you need about 75 yards of backfill material. And considering that you know the volume of material you need--2,000 cubic yards--it might make more sense to order whatever material, topsoil, gravel, or sand, by volume, not weight.
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