Concrete Mix Calculator

For a rectangular slab: multiply length × width × depth (all in the same unit). For a circular form: use π × radius² × depth. This calculator handles all shapes and converts the result to cubic yards and bag count automatically.

An 80lb bag yields approximately 0.60 cubic feet of concrete, so you need about 45 bags per cubic yard. A 60lb bag yields ~0.45 cubic feet (60 bags/yd³). A 40lb bag yields ~0.30 cubic feet (90 bags/yd³). For large projects, ordering ready-mix concrete by the truck is far more economical.

Yes — always add 10% to cover spillage, uneven sub-base depth, and mixing variation. For small or complex pours, consider 15%. Running short and having to do a second pour creates a visible cold joint (weak seam) in the finished concrete.

80lb bags yield more concrete per bag and are more economical per unit volume. 60lb bags are lighter and easier to handle, which matters when mixing by hand. 40lb bags are for small repairs and patches. All three are typically Quikrete or similar pre-mixed concrete (cement + aggregate + sand).

Ready-mix concrete delivered by truck becomes economical at around 1 cubic yard (27 cubic feet) or more. Below that, bagged concrete is usually cheaper when you factor in delivery fees. For a driveway (typically 3–4 cubic yards) or larger, always get ready-mix.

Foot traffic / patio: 4 inches (10cm). Driveway (passenger cars): 4–5 inches. Driveway (trucks / heavy vehicles): 6 inches. Garage floor: 4–5 inches. Structural footings: check local building codes — typically 8–12 inches deep.

Completely free. Enter your dimensions and get your concrete volume and bag count instantly.