Formula
Volume in cubic feet = length x width x thickness in feet. Cubic yards = cubic feet / 27. Waste allowance multiplies the final volume.
Concrete volume estimator
Concrete Calculator
Estimate how much concrete you need for a slab, patio, footing, or rectangular pour. Enter length, width, thickness, and waste allowance to calculate cubic yards, cubic feet, cubic meters, and approximate bag count.
Calculate concrete volume
Cubic yards
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Cubic feet
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Cubic meters
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80 lb bags
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Example
A 20 ft by 10 ft slab that is 4 inches thick is about 2.47 cubic yards before waste and about 2.72 cubic yards with 10% waste.
Useful for
Concrete slabs, patios, sidewalks, shed bases, garage floors, footings, and rectangular construction pours.
Concrete estimating notes
Actual concrete needs depend on site grade, compaction, form accuracy, subbase, reinforcement, and supplier yield. Round up and confirm mix requirements with your contractor or supplier.
FAQ
How much extra concrete should I order?
Many small projects add 5% to 10% waste. Irregular forms, uneven excavation, or deep spots may need more.
How many bags are in one cubic yard?
An 80 lb bag commonly yields about 0.6 cubic feet, so one cubic yard takes about 45 bags. Check the bag label for exact yield.