Concrete Calculator
Estimate concrete volume, ready-mix yards, and bag quantities for rectangular or circular projects.
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Which concrete tool fits your question?
- Concrete calculator: rectangular or circular placements from dimensions.
- Slab calculator: a quick rectangular slab with a thickness check.
- Bag calculator: known volume or rectangular slab dimensions, using your product’s listed yield.
- Cubic yard calculator: generic bulk volume, not a concrete mix recommendation.
Patio purchase planner: compare bagged mix with a complete ready-mix quote, order increments and delivery fees.
How this calculator works
Rectangle volume = length × width × depth. Circle volume = π × (diameter ÷ 2)² × depth. Cubic yards = cubic feet ÷ 27, then the waste allowance is added.
Worked example
A 12 × 10 ft rectangular pour at 4 in deep with 10% extra requires about 1.63 cubic yards.
Measure each concrete shape separately
Slabs, walls, columns, footings, and steps use different volume formulas. Calculate each placement group on its own and add the cubic feet before converting to cubic yards. Use the designed thickness rather than assuming a standard value, and measure thickened edges or turned-down sections separately.
Uneven subgrade, over-excavation, form movement, and spillage can increase the required volume. Correct the measurements first, then apply a visible ordering allowance.
Prepare for supplier questions
Ready-mix suppliers may ask for total yards, strength, slump, aggregate size, admixtures, access, placement method, and schedule. Those specifications come from the project requirements, not this volume calculator. Confirm minimum-load and short-load fees before deciding between ready mix and bagged concrete.
Sources & assumptions
Bag estimates use approximate yields of 0.45 ft³ for a 60-lb bag and 0.60 ft³ for an 80-lb bag, consistent with QUIKRETE Concrete Mix product data. Product labels and site conditions control.
Frequently asked questions
How much extra concrete should I order?
Five to ten percent is a common planning allowance for grade variation, spillage, and measurement error.
How many bags equal a cubic yard?
Yield varies by product. Using common planning yields, one cubic yard is about 60 60-lb bags or 45 80-lb bags. Check the bag label.
Concrete slab guide
Planning a small slab? See the full worked example, bag counts, and thickness table in How much concrete for a 10×10 slab?