Most slabs go down over 4–6 inches of compacted ¾" stone — either washed crushed granite or a dense-graded base blend. Washed ¾" stone drains and acts as a capillary break under the pour; Dense Pack compacts into a tighter, harder platform. Your concrete contractor's plan wins here — confirm depth and type before ordering. For a 400 sq ft pad, 4 inches of base works out to about 5 cubic yards.
Two common sub-slab choices
| Gray Granite ¾" (washed) | Free-draining, breaks capillary rise |
| Dense Pack ¾"-to-minus | Compacts dense and very stable |
Either way the math is the same: square feet × inches ÷ 324 = cubic yards. Compare Gray Granite ¾" and Dense Pack, then check totals with the material calculator.
