How Much Concrete Do I Need?
Concrete is ordered by the cubic yard for ready-mix trucks, or calculated in bags for smaller pours. One cubic yard equals 27 cubic feet. Quikrete 60lb bags yield about 0.45 cubic feet (60 bags = 1 CY). Quikrete 80lb bags yield about 0.60 cubic feet (45 bags = 1 CY).
Always add a 10% waste factor to account for spillage, uneven subgrade, and over-excavation. For ready-mix orders, round up to the nearest quarter yard — concrete trucks charge minimum delivery fees and the extra material is inexpensive compared to a second delivery charge.
Minimum Thickness Guide: Sidewalks/patios: 4 inches; Garage floors: 5-6 inches; Driveways: 5-6 inches. All concrete slabs should include reinforcement (rebar, wire mesh, or fiber reinforcement) — check local codes for requirements.
Stair Note: This calculates the stepped portion only. For solid poured-in-place stairs, add the volume of the supporting slab underneath (typically 4-6 inches thick across the full stair footprint). Actual concrete needed may be 20-40% more than shown.