Concrete Volume Calculator
Calculate concrete volume in cubic yards and cubic feet.
Calculate concrete volume in cubic yards and cubic feet.
A concrete volume calculator finds how much concrete fills a rectangular form, such as a patio slab, garage floor, shed pad, sidewalk section or wide footing. Volume is length × width × thickness. Because slab dimensions are usually measured in feet but thickness in inches, the thickness has to be converted to feet first. The result is given in cubic feet and in cubic yards, the unit ready-mix suppliers use when you place an order.
Thickness has the biggest effect on the answer. Going from a 4-inch to a 6-inch slab increases the concrete needed by 50 percent, so confirm the thickness your project or local code calls for before ordering. Uneven subgrade, form boards that bow outward and spillage all add to the real amount used, which is why contractors typically order 5 to 10 percent more than the calculated volume. Running short mid-pour can leave a cold joint, so an extra margin is usually cheaper than a second delivery. For small jobs mixed by hand, the cubic-feet figure helps estimate how many bags are needed.
To use this calculator, enter the length in feet, the width in feet and the thickness in inches, then press Calculate. The tool multiplies length by width by thickness ÷ 12 to get cubic feet, then divides by 27 to show cubic yards, rounded to two decimals. For an L-shaped or irregular area, split it into rectangles, calculate each one and add the results. For round columns, steps or sloped pours, measure and calculate those pieces separately, since this tool assumes a flat, rectangular shape of uniform thickness.
Convert the thickness to feet by dividing inches by 12, then multiply length × width × thickness to get cubic feet. Divide cubic feet by 27 to get cubic yards. Formula: cubic yards = length (ft) × width (ft) × (thickness in ÷ 12) ÷ 27.
Example: a 12 ft × 12 ft patio at 4 inches thick is 12 × 12 × (4 ÷ 12) = 48 cubic feet, and 48 ÷ 27 = 1.78 cubic yards. Adding 10 percent for waste brings the order to about 1.96 cubic yards.
Concrete needed for common slab sizes (no waste allowance)
| Slab size | Thickness | Cubic feet | Cubic yards |
|---|---|---|---|
| 4 × 4 ft | 4 in | 5.33 | 0.2 |
| 10 × 10 ft | 4 in | 33.33 | 1.23 |
| 10 × 20 ft | 4 in | 66.67 | 2.47 |
| 12 × 12 ft | 4 in | 48 | 1.78 |
| 12 × 24 ft | 4 in | 96 | 3.56 |
| 20 × 20 ft | 4 in | 133.33 | 4.94 |
| 24 × 24 ft | 4 in | 192 | 7.11 |
| 10 × 10 ft | 6 in | 50 | 1.85 |
| 12 × 24 ft | 6 in | 144 | 5.33 |
| 24 × 24 ft | 6 in | 288 | 10.67 |
Ready-mix concrete is sold by the yard. 1 cubic yard = 27 cubic feet.
Add 5–10% for waste.
It depends on thickness: one cubic yard covers about 81 sq ft at 4 inches, 64.8 sq ft at 5 inches and 54 sq ft at 6 inches. Divide 27 by the thickness in feet to get coverage for other depths.
Patios, walkways and shed floors are commonly 4 inches thick, while driveways and slabs that carry vehicles are often 5 to 6 inches. Local building codes and the project plans set the actual requirement.
A 10 × 10 ft slab at 4 inches thick needs 33.33 cubic feet, or about 1.23 cubic yards. At 6 inches it needs 1.85 cubic yards.
Divide the area into rectangles, run each one through the calculator with the same thickness, and add the cubic yards together. Then add your waste allowance to the total.
Minimum loads and short-load fees vary by supplier, so call ahead. For very small pours, the cubic-feet result can be compared with the yield printed on bagged concrete to decide whether bags are more practical.
Divide inches by 12. A 4-inch slab is 0.333 ft thick, a 5-inch slab is 0.417 ft and a 6-inch slab is 0.5 ft; this calculator does the conversion for you.
Results are estimates for planning purposes. Verify with product labels and local requirements before purchasing materials.