How do I calculate how much concrete I need for a slab?
Volume = Length × Width × Thickness (all in the same unit). For a 10 × 10 ft slab at 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.33 cubic feet ÷ 27 = 1.23 cubic yards. Always add 5–10% for waste, spillage, and uneven ground. Typical slab thicknesses: 4 inches for residential driveways and patios, 6 inches for heavy vehicle traffic or garage floors.
What is a cubic yard of concrete and how much does it cover?
One cubic yard = 27 cubic feet. At 4 inches thick, 1 cubic yard covers 81 sq ft (roughly a 9×9 ft area). At 6 inches thick, 1 cubic yard covers 54 sq ft. At 3.5 inches (standard slab), 1 yard covers approximately 93 sq ft. Ready-mix concrete is ordered by the cubic yard; a standard ready-mix truck holds 8–10 cubic yards.
What concrete mix do I need for a driveway or patio slab?
The most common residential mix is 3,000 psi (pounds per square inch) — typically a 1:2:3 ratio of cement:sand:gravel with a 0.5 water-to-cement ratio. For driveways subject to vehicle traffic, use 4,000 psi. In freezing climates, use air-entrained concrete with 6% air content to resist freeze-thaw cracking. For footings and structural work, 4,000 psi or higher is typically required by building codes.
How deep should a concrete slab be?
Minimum slab thickness depends on use: Sidewalks and garden paths: 3–4 inches. Patios and residential driveways: 4 inches. Garage floors (car storage): 4–6 inches. Commercial or heavy vehicle areas: 6–8 inches. Structural footings: Typically 8–12 inches or per structural engineer's specification. In frost-prone areas, footings must extend below the frost line (up to 4 ft deep in northern climates) to prevent frost heave.
Should I use ready-mix concrete or mix my own?
For projects under 0.5 cubic yards, mixing your own (bags) is cost-effective — an 80 lb bag yields roughly 0.6 cubic feet. For larger pours (0.5+ cubic yards), ready-mix delivery is more economical and produces consistent quality. Ready-mix costs roughly $125–$175 per cubic yard (2024 US prices) plus delivery. DIY mixing from bags runs about $5–$6 per cubic foot in materials. Always order 5–10% extra to avoid running short mid-pour.