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Estimate volume, waste, and bag count for a slab, footing, or path.
Enter your numbers to see the answer.
Concrete calculator guide
A concrete estimate starts with the space you are filling: length, width, and finished depth. This calculator converts the depth from inches to feet, multiplies the three dimensions to find cubic feet, adds your waste allowance, and shows the result in cubic yards. That sequence matters because ready-mix concrete is commonly ordered by the cubic yard, while the measurements on a tape measure are often a mix of feet and inches. Use the planned concrete depth, not the thickness of the gravel base below it. For a slab, measure the inside length and width of the pour area. For a footing or path, use the actual run of concrete. The result is a planning estimate, so confirm access, minimum delivery quantities, product yield, and site conditions with the supplier before placing an order.
Base volume (ft³) = length (ft) × width (ft) × depth (in) ÷ 12. Adjusted volume (yd³) = base volume (ft³) × (1 + waste ÷ 100) ÷ 27.
Worked example: a 10 ft × 10 ft slab that is 4 in deep has a base volume of 10 × 10 × (4 ÷ 12) = 33.33 ft³. Convert to yards: 33.33 ÷ 27 = 1.23 yd³. With 10% waste, 33.33 × 1.10 = 36.67 ft³, or 36.67 ÷ 27 = 1.36 yd³. The calculator also estimates 62 80 lb bags using a 0.6 ft³ yield per bag; actual bag yield varies by product.
Enter length and width in feet and depth in inches, as labeled. Four inches is 4 ÷ 12 = 0.333 ft. Do not multiply feet by inches without converting first. One cubic yard equals 27 cubic feet, and the calculator uses 0.0283168 cubic meters per cubic foot for the metric display.
Good to know: waste covers small measurement errors, spillage, uneven forms, and site loss; it does not correct a wrong depth or an undersized form. Measure the finished pour, keep all dimensions consistent, and round a purchase up rather than down when a shortage would stop the job.
Results are planning estimates. Check the units, product coverage, carrier rules, or local rates before making a purchase or financial decision.
How it works
Estimate volume, waste, and bag count for a slab, footing, or path. This tool explains the calculation so you can adjust the assumptions to match your situation.
Common questions
At 4 inches deep, a 10 ft × 10 ft slab needs about 1.23 cubic yards before waste and about 1.36 cubic yards with 10% waste. Enter your own depth and allowance for a closer estimate.
Multiply length by width by depth in feet to get cubic feet, apply any waste allowance, then divide by 27. Convert inches to feet before multiplying.
A modest waste allowance is useful for uneven ground, spillage, and small measuring errors. The right percentage depends on the shape and site; confirm the final quantity with the concrete supplier.
Yes, but convert the inches to feet first. The calculator accepts feet for length and width and inches for depth, then performs that conversion for you.
Divide the adjusted cubic feet by the bag yield. This page uses 0.6 ft³ per 80 lb bag as a sample yield and rounds up; check your product label because yields differ.