Calculate concrete volume in cubic yards and 80-lb bags for slabs, pads and rectangular pours using length, width, thickness and extra allowance.
Enter your measurements and material details.
Do not order the exact mathematical volume for a ready-mix pour; uneven subgrade and spillage can leave you short.
The concrete calculator estimates the volume of a rectangular slab or pad, converts it to cubic yards for ready-mix ordering, and provides an approximate 80-pound bag count for smaller jobs. The bag estimate assumes roughly 0.6 cubic feet of yield per bag; always check the product label because yields vary.
Measure form dimensions after excavation and base preparation when possible. Thickness has a large effect on total volume: a slab that is one inch thicker than planned can add substantial concrete over a large area. Irregular excavations should be divided into simpler shapes or measured conservatively.
There are 27 cubic feet in one cubic yard.
A practical allowance is often 5–10%, depending on form accuracy, subgrade variation and job size.
At about 0.6 cubic feet per bag, one cubic yard is roughly 45 bags, but actual package yield must be checked.
Yes for a rectangular driveway section, provided you enter the planned finished thickness.
No. Reinforcement, joints, base preparation and structural design are separate decisions.
Using the example inputs shown in the calculator — Length (ft) = 12, Width (ft) = 10, Thickness (in) = 4, Extra allowance (%) = 8 — the result is 1.6 cubic yards. This demonstrates the formula with a complete set of numbers rather than a hidden assumption.
The result breakdown also shows Raw volume: 1.48 yd³; 80-lb bags: 73. Replace the example values with field measurements and the exact product coverage, yield or package size you plan to buy.
For this concrete calculator, the inputs with the greatest practical effect are length, width and thickness. Recalculate when any of those change; do not reuse a result from a different room, run, layer depth or product specification.
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