Concrete Calculator
Free concrete calculator — estimate cubic yards or meters and bags of concrete needed for slabs, footings, columns, and post holes.
Everyday Uses
Slab pours
Patio, driveway, or shed base — get cubic meters or yards and the number of bags to order.
Fence post setting
Calculate concrete per post hole and total bags for the whole fence line.
Budgeting the job
Concrete is priced by volume — accurate math prevents both shortfall and waste.
Bag math
Convert volume into 40/60/80 lb bags so the store trip happens exactly once.
Frequently Asked Questions
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.