A compacted gravel base under a concrete slab does two jobs: it provides drainage so water does not pool under the concrete, and it creates a stable, evenly-compactable surface so the slab does not settle unevenly and crack. This calculator uses the same volume math as a concrete slab — length × width × depth — but converts the result into both cubic yards, which is how landscape supply yards often quote bulk gravel, and tons, which is how it is frequently sold and hauled by the truckload.

The tonnage conversion uses a typical density of roughly 2,700 lb per cubic yard for compacted crushed stone or road base, which is a reasonable planning estimate for most 3/4 in minus gravel. Exact weight varies with the specific material and how wet it is, so always confirm with your supplier before finalizing an order, especially on larger jobs where the difference adds real cost.