Construction calculator
Concrete Calculator
Estimate concrete volume for a rectangular slab.
About the concrete calculator
The concrete calculator estimates how much concrete you need for a rectangular slab, foundation, or patio. Enter the length, width, and depth to get the volume in cubic yards — the standard unit for ordering ready-mix concrete.
How to use this calculator
- 1
Measure length and width
Measure the slab dimensions in feet.
- 2
Measure depth
Measure the desired thickness in inches (typically 4 inches for driveways, 6 inches for heavy loads).
- 3
Calculate volume
Volume = length × width × (depth ÷ 12) ÷ 27 for cubic yards. Add 5–10% for waste.
How the calculation works
Convert depth from inches to feet, multiply by length and width, then divide cubic feet by 27 for cubic yards.
Example: A 10 × 10 ft slab at 4 inches deep needs about 1.23 yd³ before waste allowance.
How much concrete do I need?
A standard residential driveway (20 × 20 ft at 4 inches deep) needs about 4.9 cubic yards. A patio of the same size needs the same amount. Always order 5–10% extra to account for spillage, uneven subgrade, and form variations. Concrete is typically sold in quarter-yard increments.
Why use construction calculators?
Construction projects involve significant material costs. Overestimating wastes money; underestimating causes delays. These calculators use standard industry formulas to give you reliable estimates for concrete, lumber, drywall, paint, roofing, flooring, and more. Always add 5–15% waste allowance for cuts, mistakes, and irregularities.
How to get accurate results
Measure twice, calculate once. Use a tape measure for dimensions, and enter values in the units shown. For irregular shapes, break the area into rectangles and calculate each separately. When in doubt, round up — it's better to have a little extra material than to run short mid-project.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about concrete calculator
How accurate is the concrete calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.