How to Calculate Concrete for a Slab or Footing

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Calculating concrete for a slab or footing is straightforward: multiply length by width by thickness (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards. For a 20' x 10' x 0.33' slab, that's 66 cubic feet, or about 2.5 yards. Always add 10% extra for waste or uneven ground.