Concrete Calculator
Estimate concrete volume in cubic yards and ready-mix bag counts for slabs, footings, rectangular piers, and simple stairs.
Last updated: 2026-03-18
Concrete calculator
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Estimate cubic yards and ready-mix bag counts for slabs, footings, rectangular piers, and simple stairs.
Recommended order
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Enter your dimensions to estimate the pour volume, then check whether ready-mix bags or a yardage order makes more sense.
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Example calculations
Tap an example to prefill the calculator with sample values.
Small patio slab
12 ft x 10 ft x 4 in
A common patio pour where bag count is still realistic but yardage is easier to sanity-check.
Result: About 1.63 cubic yards with waste, or 74 eighty-pound bags
Three rectangular piers
8 ft tall, 18 in x 18 in, quantity 3
Useful for deck or pergola planning when you need a rectangular pier estimate rather than a round sonotube.
Result: Roughly 2.20 cubic yards with the built-in waste buffer
Simple six-step stair pour
4 ft wide, 11 in run, 7 in rise, 6 steps
A quick wedge estimate for basic exterior steps before more detailed formwork adjustments.
Result: A small pour at about 0.26 cubic yards with waste
How the concrete estimate works
Concrete volume depends on the actual shape being poured, not just the outer footprint. Slabs and footings are simple rectangles, rectangular piers behave like boxes, and stairs are estimated here as repeated wedge volumes rather than solid blocks.
The output includes a built-in 10 percent waste allowance to reduce the odds of coming up short. It is still a planning tool, so unusual forms, round columns, and supplier-specific mixes should be confirmed before you order.
Concrete calculator FAQs
How to interpret cubic yards, bag counts, and the built-in waste buffer.
Why does the calculator show both cubic yards and bag counts?
Concrete suppliers usually quote larger pours in cubic yards, while smaller DIY jobs are often done with 60-pound or 80-pound bags. Showing both helps you decide which route makes more sense for the size of the pour.
Why is there a waste buffer?
Small spills, uneven forms, and over-excavation can all increase the real amount of concrete you need. This calculator adds a standard 10 percent waste allowance so the order is less likely to come up short.
Does this work for round columns or sonotubes?
Not exactly. The column mode in this version assumes a rectangular pier. Round columns and sonotubes need cylinder math, which should be handled as a follow-up expansion rather than guessed here.
Why do stairs use less concrete than a same-size slab?
The stair estimate uses a wedge-style approximation rather than filling the full rectangular box around the steps. That is why the volume is much smaller than a slab with the same outer dimensions.
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