Concrete Calculator
Calculate how much concrete you need for slabs, footings, columns, and walls. Enter your project dimensions and choose between bulk cubic yards or bagged concrete for instant results.
How to Calculate Concrete
The concrete volume formula converts your project dimensions into cubic yards:
- Measure the area you want to pour in feet (length and width).
- Determine the thickness in inches. Standard slabs are 4 inches thick.
- Calculate volume: Length (ft) × Width (ft) × Depth (in) ÷ 12 ÷ 27 = Cubic Yards.
- Convert to bags: Divide cubic yards by the yield per bag to get the number of bags needed.
Concrete Thickness Guide
- 4 inches: Sidewalks, patios, shed floors, and standard slabs
- 6 inches: Driveways, garage floors, and areas with vehicle traffic
- 8 inches: Foundation walls and structural elements
- 12 inches: Footings, load-bearing foundations, and columns
Concrete Types and Uses
- Standard mix (2,500 PSI): General-purpose use for walkways and patios
- Crack-resistant (4,000 PSI): Driveways and garage floors
- High-strength (5,000+ PSI): Footings, foundations, and structural work
- Fast-setting: Post holes, small repairs, and cold-weather pours
How many bags of concrete do I need for a 10x10 slab?
A 10 ft by 10 ft slab at 4 inches thick is a useful benchmark because it is close to the point where bagged concrete starts to feel like a lot of lifting.
- Area: 10 × 10 = 100 square feet.
- Volume: 100 × 4 inches ÷ 12 = 33.3 cubic feet.
- Cubic yards: 33.3 ÷ 27 = 1.23 cubic yards.
- Bag estimate: about 56 bags of 80 lb mix, 72 bags of 60 lb mix, or 112 bags of 40 lb mix.
For a slab around this size, compare bag cost, delivery access, and mixer rental against a small ready-mix order. Ready-mix is often easier once the project is above roughly one cubic yard.
Concrete calculator for round columns
For a round pier, post footing, or column, use a cylinder formula instead of the rectangular slab formula: 3.1416 × radius² × height. Keep radius and height in feet before converting to cubic yards.
Example: a 12 inch diameter column that is 4 feet deep has a 0.5 ft radius. The volume is 3.1416 × 0.5 × 0.5 × 4 = 3.14 cubic feet, or about 0.12 cubic yards before waste. Add a little extra if the hole is rough, bell-shaped, or wider at the top.