Concrete slab & footing calculator
Estimate the concrete volume for a rectangular slab or footing in cubic yards (for ready-mix delivery) and in 40/60/80 lb bags (for small pours). Add an overage so you don't run short mid-pour.
2.72 cubic yards
Concrete (ready-mix)
- Total volume
- 73.3 cubic feet
- 80 lb bags
- 123 bags
- 60 lb bags
- 163 bags
- 40 lb bags
- 245 bags
What this assumes
- Volume = 20 ft × 10 ft × 4.0 in, +10% overage.
- Bag counts use published yields: 80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³.
- For pours over ~1 cubic yard, ready-mix delivery is usually cheaper than bags.
Coverage rates & sources
Every number this calculator uses is a published engineering constant — not an estimate we made up. Here is exactly what it assumes and where each value comes from.
- 80 lb bag yield: 0.60 ft³Source: Quikrete / Sakrete concrete mix bag specifications
- 60 lb bag yield: 0.45 ft³Source: Quikrete / Sakrete concrete mix bag specifications
- 40 lb bag yield: 0.30 ft³Source: Quikrete / Sakrete concrete mix bag specifications
- Cubic yard: 27 ft³Source: Unit conversion (3 ft × 3 ft × 3 ft)
Before you buy
- Rectangular slabs/footings only — for steps, curbs, columns, or irregular shapes, add each section separately.
- Does not include rebar, wire mesh, gravel base, or form lumber.
- Order ready-mix to the quarter-yard; a supplier or contractor should confirm before a large pour.
This is a planning estimate, not a substitute for a pro's on-site measurement. For load-bearing, structural, or code-regulated work, confirm quantities with a licensed contractor.
Frequently asked
How thick should a concrete slab be?
4 inches is standard for patios, walkways, and shed pads. Driveways and areas with vehicle loads are typically 5–6 inches over a compacted gravel base. A pro should confirm for structural or load-bearing work.