How to use this concrete calculator
Enter the requested values above and select Calculate. The result updates immediately on the page, so you can change one value and compare different scenarios without leaving the calculator.
Formula and method
Example
A 20×10 ft slab at 4 inches thick needs about 2.47 yd³ before waste.
What this calculator is useful for
Estimate cubic yards of concrete for a rectangular slab and add an optional waste allowance. It is designed for quick estimates and everyday problem solving. When a calculation affects a contract, tax filing, medical decision or other high-stakes situation, verify the result with the appropriate professional or authoritative source.
Frequently asked questions
What does the Concrete Calculator calculate?
Estimate cubic yards of concrete for a rectangular slab and add an optional waste allowance.
How does the calculation work?
Cubic yards = length × width × (thickness ÷ 12) ÷ 27, then increased by the waste allowance.
Is this calculator free?
Yes. ERICH Calculators is free to use and no account is required.