Concrete Slab Calculator

Concrete slab calculator

Enter each slab, patio, path or pad. You get the total in cubic yards, the amount to order with waste, and the bag count for 40, 60 and 80 lb premix.

Concrete to order

Premix bagBagsTotal weight

Check local building code and the manufacturer's instructions. Structural and roofing work may need a permit or a professional.

Tools and materials for this job

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How the numbers are worked out

  1. Measure each section. Measure the length and width in feet and the thickness in inches. Split an L-shaped or stepped slab into rectangles.
  2. Work out the volume. Multiply length by width by thickness in feet (inches divided by 12) for cubic feet, add up the sections, and divide by 27 for cubic yards. A 10 x 10 ft slab 4 inches thick is 33.3 cubic feet, or 1.23 cubic yards.
  3. Add waste. Add an allowance for spillage, an uneven base and form flex. 10% is a common figure. Round a ready-mix order up to the next quarter yard.
  4. Count the bags. Divide the cubic feet, with waste, by the yield on the bag and round up. An 80 lb bag of premix yields about 0.60 cubic feet, a 60 lb bag 0.45 and a 40 lb bag 0.30.

Bag yields are the figures printed by the maker and are approximate. Check the bag you buy, since mixes differ. Order a little extra rather than run short partway through a pour.