Shopping estimate
Use the yield printed on your bag. Ready-mix pricing uses the larger of the estimated volume and your supplier minimum. Confirm order increments and fees with your supplier.
Worked examples
10 × 12 ft shed slab, 4 inches thick. The slab takes 40 ft³ before waste. With 10% extra, allow 44 ft³, or about 1.63 yd³. At 0.60 ft³ per bag, round up to 74 bags.
Patio plus walkway. A 10 × 12 ft patio and a 3 × 15 ft walkway, both 4 inches thick, take 55 ft³ before waste. With 10% extra and 0.60 ft³ per bag, plan for 101 bags.
For each section, multiply length × width × thickness ÷ 12. Sum the volumes, add waste, and divide by 27 for cubic yards. This tool estimates quantities. Enter the thickness specified for your project.