Concrete Calculator

Estimate the concrete you need for a slab, footing or pad — in cubic yards (for ready-mix delivery) and in bags (for small DIY pours).

How the Math Works

The Concrete Calculator uses a formula to determine the volume of concrete needed for a slab. First, it calculates the slab's volume in cubic feet by multiplying length (in feet) by width (in feet) by thickness (converted from inches to feet by dividing by 12). This result is then divided by 27 to convert cubic feet to cubic yards, as 1 cubic yard equals 27 cubic feet. Finally, the formula multiplies by (1 + waste percentage) to account for spillage or over-application, ensuring enough material is ordered to complete the project without delays.

Practical Applications

To use this calculator, measure the slab's length and width in feet and its thickness in inches. Input these values along with an estimated waste percentage (typically 5-15%) into the tool. The result provides the total cubic yards of concrete required and the number of bags needed, based on standard bag sizes (e.g., 80 lb bags covering 0.6 cubic feet each). This helps in ordering the correct amount of materials, avoiding shortages or excess purchases that could waste money or time.

Day-to-Day Use

This calculator simplifies everyday construction tasks, such as building a patio, driveway, or garage floor, by providing precise material estimates. By factoring in waste, it prevents costly last-minute trips to the supplier and ensures projects stay on schedule. It also aids in budgeting, as users can quickly calculate costs based on local concrete prices per cubic yard, making DIY projects more manageable and financially predictable.

Worked example

10×10 ft slab, 4 in thick, 10% waste → 36.7 ft³ = 1.36 yd³ (≈82 × 60 lb bags).

FAQ