Concrete Calculator
Find cubic yards of concrete for slabs, footings, columns, walls, and circular pads. Includes cubic feet, cubic meters, bags, waste, and how much to order.
How to use this concrete calculator
Ready-mix plants sell concrete in cubic yards. A cubic yard is 27 cubic feet — a 3×3×3 ft cube. For a slab, convert thickness from inches to feet (4 in = 0.333 ft), multiply length × width × thickness, then divide by 27. Add 5–10% waste for uneven subgrade and spillage.
This concrete calculator covers the five pours homeowners actually order: rectangular slabs, footings, walls, round piers, and circular pads. Patio and sidewalk slabs are usually 4 in; driveways and garage floors 5–6 in; footings follow the frost line on your plan. Bags (80 lb ≈ 0.60 cu ft) are only cheaper under about one yard.
Formula
Worked example
A 10×10 ft slab, 4 in thick, with 10% waste is 10×10×(4/12)×1.10 = 36.67 cu ft = 1.36 cubic yards (order 1.5). That is about 1.04 m³ or 62 bags of 80 lb mix.
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Frequently asked questions
How do I calculate cubic yards of concrete?
Length × width × thickness in feet, then divide by 27. A 10×10×4″ slab is 10×10×0.333 = 33.3 cu ft ÷ 27 ≈ 1.23 yards before waste.
How much concrete do I need for a 10×10 slab?
At 4 inches with 10% waste, about 1.36 cubic yards. Order 1.5 yards from the truck.
How thick should a concrete slab be?
Patios and sheds: 4 in. Driveways and garage slabs: 5–6 in on a compacted base. Follow the engineer for structural work.
How many 80 lb bags in a yard?
About 45 bags. Mixing more than a yard by hand is miserable — call a truck.
Cubic feet to cubic yards?
Divide cubic feet by 27. Multiply cubic yards by 0.7646 for cubic meters.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-19.