Concrete calculator
For slabs, footings, and pads. Get cubic yards for a ready-mix order, or bags if you're mixing it yourself.
Slab or footing details
How this is calculated
Volume starts as length × width × thickness, with thickness converted from inches to feet: length × width × (thickness ÷ 12). That gives cubic feet. A 10% waste margin is added for spillage, uneven subgrade, and minor form overfill, which is standard for a straightforward rectangular pour. Cubic feet is then divided by 27 to convert to cubic yards — the unit ready-mix trucks price by. If you're mixing bags by hand instead, the same cubic footage (with waste included) is divided by the bag's yield to get a bag count.
How much concrete for a 10×10 patio?
At a standard 4" thickness, a 10×10 slab needs roughly 1.4 cubic yards, or about 28 bags of 60 lb concrete mix — hand-mixing that many bags is a full day of work for one person, so most people order ready-mix past about 1 yard.
Cubic yards or bags — which is cheaper?
Ready-mix is almost always cheaper per cubic yard once you're above roughly 1–1.5 yards, since bagged concrete carries a per-bag markup. Below that, most ready-mix suppliers charge a short-load fee that can make bags the better deal.
Do footings need a different waste margin?
Footings poured against undisturbed soil (rather than forms) often use closer to 15% waste, since the trench walls aren't perfectly straight. Add a bag or two, or round your ready-mix order up to the next quarter yard.
Once you know how much to order
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60 lb concrete mix
Yields ~0.45 cu ft per bag, matches the default above.
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