Concrete Calculators

How to estimate concrete

Estimating concrete comes down to one thing: volume. Every pour — a slab, a footing, a wall, a round column, or a flight of stairs — is a shape whose volume you work out in cubic feet, then convert to cubic yards by dividing by 27. The geometry differs (a slab is length × width × thickness, a column is π × radius² × height, stairs stack step by step), which is why each calculator above is tuned to its element, but the output is always the same: how much concrete you need.

Once you have the volume, you have two ways to buy it. Ready-mix, delivered by the truck and priced by the cubic yard, is cheaper and far less work past about half a yard — and it’s the only practical option for a continuous pour like a wall or a large slab. Bags of dry mix make sense for small jobs: an 80-lb bag yields about 0.6 cubic feet, a 60-lb about 0.45, and a 40-lb about 0.3. Each calculator shows both the cubic yards and the bag count for all three sizes, so you can compare.

Whatever you pour, order about 10% extra — you can’t pause a pour to mix more, and the subgrade is never perfectly level. Most slabs and footings also sit on a compacted gravel base; size that with the gravel or crushed stone calculator. Structural work — walls, footings, anything carrying a load or over a few feet — generally needs rebar and a permit, so check your local code before you build.