Concrete Volume Calculator
Calculate how much concrete you need for a slab, footing, wall, or round column — in cubic yards, cubic metres, and 60/80 lb bags. Imperial or metric, with a waste allowance. Free, no sign-up.
How many identical pours
For volumes above ~1 yd³, ready-mix delivery is almost always cheaper and faster than bags. Order to the next quarter-yard.
What this calculator does
It turns the dimensions of a pour into the amount of concrete you need to order — in cubic yards, cubic feet, and cubic metres, plus an estimate of 60 lb and 80 lb bags if you're mixing on site. Pick a rectangular shape for slabs, footings, and walls, or a round column for piers and sonotubes.
How to use it
Choose your unit system, then the shape. For a slab, enter length and width in feet (or metres) and the thickness in inches (or millimetres) — that mixed-unit convention matches how slabs are actually specified. For a column, enter the diameter and height. Set the quantity if you're pouring several identical pieces, add a waste percentage, and read the order figure off the top result card.
The formulas
Rectangular: volume = length × width × thickness.
Round column: volume = π × radius² × height.
Cubic feet ÷ 27 gives cubic yards; cubic feet × 0.0283 gives cubic metres. Bag counts come from each bag's yield — 0.45 ft³ for a 60 lb bag, 0.60 ft³ for an 80 lb bag — rounded up to whole bags.
What the numbers mean
The highlighted figure is what to order, with your waste allowance baked in. Ready-mix is sold by the cubic yard (or metre) and most suppliers have a minimum load and short-load fees, so round up to the next quarter-yard. The bag counts are there for small jobs — once you're over a yard, the bag route is slower and pricier than a delivery.
Practical tips
- Measure the form, not the plan. Subgrade is rarely dead flat; an over-dug footing holds more concrete than its nominal dimensions.
- Pour continuously. Running out mid-slab creates a cold joint. The waste percentage exists to prevent exactly that.
- Confirm the mix. Strength (e.g. 25 or 32 MPa / 3,000 or 4,000 psi) doesn't change the volume, but it does change the price and the order.
Go deeper
Want the reasoning behind these numbers and a few worked examples? How much concrete do I need? Slabs, footings, and columns walks through it the way I estimate a pour on site.
Frequently asked questions
How many bags of concrete are in a cubic yard?▾
A cubic yard is 27 cubic feet. An 80 lb bag yields about 0.60 ft³, so you need roughly 45 bags per cubic yard; a 60 lb bag yields about 0.45 ft³, or about 60 bags per yard. Bagged concrete gets expensive fast — past about one cubic yard, ready-mix delivery is almost always cheaper.
How much extra concrete should I order?▾
Add 5–10% for waste, spillage, and uneven subgrade. Slabs poured on rough ground or over-excavated footings can swallow more, so lean toward 10%. Running short mid-pour means a cold joint or a second delivery charge — over-ordering slightly is the cheaper mistake.
What's the formula for concrete volume?▾
For a rectangular slab or footing: volume = length × width × thickness, with all three in the same unit. For a round column: volume = π × radius² × height. This calculator keeps length and width in feet (or metres) and thickness/diameter in inches (or millimetres), then converts everything to cubic yards, cubic feet, and cubic metres.
How thick should a concrete slab be?▾
Four inches (100 mm) is standard for patios, walkways, and residential floors. Driveways and areas carrying vehicle loads usually go to 5–6 inches (125–150 mm). Thicker slabs need proportionally more concrete — double-check the thickness before ordering, since it drives the volume linearly.
Does this account for rebar or voids?▾
No — it calculates the gross volume of the form. Rebar displaces a negligible amount and is ignored by convention. If your pour has large block-outs or embedded voids, calculate those separately and subtract.
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