Construction Tools
Calculate concrete volume needed for a slab. Enter dimensions, select your unit, and get instant results in cubic yards, cubic metres, and bag quantities.
Concrete Volume
1.23 cubic yards
Concrete volume is the total amount of concrete required to fill a slab. It is calculated as length times width times thickness. For example, a slab that is 10 feet long, 10 feet wide, and 4 inches thick requires 1.23 cubic yards of concrete. Knowing the exact volume prevents over-ordering and waste.
Select your unit system (feet-inches or metres). Enter the length, width, and thickness of your slab. The calculator multiplies these dimensions to find total volume in cubic feet, then converts to cubic yards and cubic metres. It also estimates the number of 60lb and 80lb bags needed, assuming standard bag yields.
Volume = Length × Width × Thickness; then convert: 1 cubic yard = 27 cubic feet; 1 cubic metre ≈ 1.31 cubic yards; Bags = Volume ÷ Bag Size in cubic yardsMultiply all three dimensions together to get cubic feet. Divide by 27 to convert to cubic yards (standard in the US). Multiply cubic yards by 0.765 to get cubic metres. An 80lb bag covers about 0.6 cubic feet, so divide volume in cubic yards by 0.6 to get bag count. A 60lb bag covers about 0.45 cubic feet per yard, so divide by 0.45 for that total.
| Input | Result | Notes |
|---|---|---|
| 10 ft × 10 ft × 4 in slab | 1.23 cubic yards | Volume = (10 × 10 × 0.333) ÷ 27 = 1.23 yd³; 80lb bags ≈ 2; 60lb bags ≈ 3 |
| 20 ft × 15 ft × 6 in slab | 5.56 cubic yards | Volume = (20 × 15 × 0.5) ÷ 27 = 5.56 yd³; 80lb bags ≈ 9; 60lb bags ≈ 12 |
| 5 m × 4 m × 0.15 m slab | 3.94 cubic yards | Volume = 5 × 4 × 0.15 = 3 m³ ≈ 3.94 yd³; 80lb bags ≈ 7; 60lb bags ≈ 9 |
Most driveways and patios are 4 inches thick. Heavy-traffic areas or loading docks may need 6 inches. Thin slabs (less than 3 inches) crack easily.
An 80lb bag covers about 0.6 cubic feet. Use the calculator to find your volume, then divide by bag size. Round up because it is better to have extra.
This calculator is designed for rectangular slabs. For irregular shapes, break them into rectangles, calculate each, and add the results.
An 80lb bag covers more area (about 0.6 cu ft) than a 60lb bag (about 0.45 cu ft). 80lb bags are more economical but heavier to handle.
Yes. Concrete suppliers recommend 5–10% extra for spillage, settling, and waste. It is cheaper than running short and halting your project.
This calculator is accurate for rectangular slabs with uniform thickness. Real projects may have slight variations; add 10% as a buffer.