Concrete Calculator
Estimate how much concrete a slab, footing or pad needs. Enter the dimensions and the calculator returns the volume in cubic yards and the number of pre-mix bags — including a waste allowance.
How it works
Volume (cu ft) = length × width × (thickness ÷ 12). Cubic yards = cu ft ÷ 27. Bags = cu ft ÷ bag yield (80 lb = 0.60 cu ft, 60 lb = 0.45, 40 lb = 0.30), rounded up, plus your waste allowance.
Frequently asked questions
How many 80 lb bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet, and an 80 lb bag yields about 0.60 cubic feet, so a cubic yard takes roughly 45 bags of 80 lb concrete.
How thick should a concrete slab be?
Patios and walkways are usually 4 inches thick; driveways and slabs that carry vehicles are typically 5–6 inches. Always follow local code for structural work.
Should I order a little extra concrete?
Yes — a 5–10% waste allowance covers spillage, uneven subgrade and over-excavation. This calculator adds your chosen waste percentage automatically.
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Estimates are for planning only. Material yields, densities and code requirements vary — confirm quantities with your supplier and local building code before ordering.