Gravel Cost Calculator

Concrete Calculator

Estimate how many cubic yards of ready-mix concrete — or how many 80 lb bags — you need for a slab, footing, or walkway.

Pick the shape that best matches your slab, footing, or walkway.

ft
ft
in

Most slabs use 4 in; driveways and footings often use 5–6 in.

Covers spillage, uneven forms, and over-excavation. 10% works for most slabs.

How this is calculated

Area is calculated from the shape you select — rectangle (length × width), circle (π × radius²), triangle (½ × base × height), circular ring (π × (outer radius² − inner radius²)), or trapezoid (average of the two parallel sides × width). That area is multiplied by thickness to get volume, converted from cubic feet to cubic yards (27 ft³ per yd³). Ready-mix trucks are typically ordered in quarter-yard increments, so the recommended order is rounded up accordingly. The bag estimate assumes standard 80 lb bags of concrete mix, each yielding about 0.6 ft³ once mixed. Weight assumes standard concrete at approximately 150 lb per cubic foot. We add your selected waste percentage to cover spillage, uneven forms, and over-excavation.

Example calculation

A 10 ft × 10 ft slab at 4 in thick needs 1.23 yd³ of concrete. With 10% waste that's 1.36 yd³, so order 1.5 yd³ from a ready-mix truck — or about 62 bags of 80 lb mix.

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Frequently asked questions

Yes. Use the "Slab shape" dropdown to switch to circle, triangle, circular ring, or trapezoid. Each shape shows the measurements it needs and the area formula used is shown in the breakdown.