Concrete & construction
Concrete Yard Calculator
Convert a slab's dimensions into the cubic yards of concrete to order, with waste included.
Result
Concrete is ordered by the cubic yard and delivered in fixed increments, so the figure you order is always rounded up. Most crews add 5% to 10% for spillage, uneven subgrade and over-excavation; running short mid-pour is far more expensive than a little waste.
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About this calculator
How many cubic feet in a yard of concrete?
Twenty-seven. A cubic yard is three feet by three feet by three feet, which is the conversion every concrete quantity depends on.
How much waste should I allow?
Between 5% and 10% on a prepared subgrade, more if the ground is uneven or the forms are rough. Being a quarter yard short with the truck leaving is a cold joint, which is a permanent defect.
What thickness does a slab need?
Four inches is typical for a patio or footpath, five to six for a driveway carrying vehicles, and more for anything heavier. Local code and the soil underneath decide it, not the span.
The formula
cubic yards = length x width x (thickness / 12) / 27
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