Concrete Slab Calculator
Rectangular Slab
Calculate concrete volume for a rectangular slab
ft
ft
in
$
Formula
Volume (cu yd) = (Length × Width × (Thickness ÷ 12)) ÷ 27 × 1.10 waste factor
Frequently Asked Questions
How do I calculate concrete for a slab?
Multiply length x width x thickness (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards. Add 10% extra for waste and spillage.
How many bags of concrete do I need?
An 80-lb bag of premixed concrete yields about 0.6 cubic feet. Divide your total cubic feet by 0.6 to get the number of 80-lb bags. For a 60-lb bag, divide by 0.45; for a 40-lb bag, divide by 0.3.
What is a standard slab thickness?
Most residential concrete slabs are 4 inches thick. Garage slabs and driveways are typically 5-6 inches. Heavy-duty industrial slabs may be 6-8 inches or more.
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