Estimate how much concrete you need for a slab, footing, or column, in cubic yards, cubic meters, and bags.
For a slab or rectangular pad, volume is length × width × thickness. For a round column or footing, volume is π × (diameter ÷ 2)² × height. This calculator converts your inputs into cubic feet first, then reports the total in cubic yards and cubic meters, since ready-mix concrete is usually ordered by the cubic yard (or cubic meter outside the US).
For small jobs — fence posts, a shed pad, a few stepping stones — pre-mixed bags from a hardware store are usually more practical than ordering a truck. This calculator estimates bag counts assuming a 60 lb bag yields about 0.45 cubic feet of cured concrete and an 80 lb bag yields about 0.6 cubic feet, which are standard manufacturer figures.
Concrete calculations should always be padded, not rounded down. Uneven ground, formwork gaps, and spillage typically use 5–10% more material than the "on paper" volume, and running short mid-pour creates a cold joint that weakens the slab. Most contractors order at least 10% extra for exactly this reason.
| Project | Typical thickness |
|---|---|
| Shed / patio slab | 4 in |
| Driveway | 5–6 in |
| Sidewalk | 4 in |
| Fence post footing | Full post depth |
This tool gives a planning estimate only — always confirm quantities with your supplier or contractor before ordering.