The formula for concrete is straightforward:
(Length in ft) × (Width in ft) × (Depth in inches ÷ 12) ÷ 27 = cubic yards needed
Then add 10% for waste, spillage, and uneven subgrade. For a 12 × 14 ft patio at 4 inches deep, that's 12 × 14 × (4/12) ÷ 27 = 2.07 cubic yards, or 2.3 cubic yards with overage.
For irregular shapes, break the area into rectangles, triangles, and circles, calculate each separately, then add the results. The calculator below handles common shapes automatically.
A few rules of thumb if you don't have exact dimensions: • A standard 1-car driveway (10 × 20 ft, 4 in deep) needs about 2.5 cubic yards • A standard 2-car driveway (20 × 24 ft, 4 in deep) needs about 6 cubic yards • A 12 × 12 ft patio at 4 in needs 1.8 cubic yards • A standard 4-inch sidewalk needs 1 cubic yard per 81 linear feet at 3 ft wide