Order 5-10% extra to account for spillage and subgrade variance.
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Concrete is typically ordered by the cubic yard for ready-mix truck delivery, or by the bag (60lb or 80lb pre-mixed bags) for smaller DIY projects. Always order 5-10% extra to account for spillage, uneven subgrade, and measurement variance.
Worked Example
Example: A 10ft × 10ft slab, 4 inches deep = 100 sq ft × 0.333 ft = 33.3 cubic feet = 1.23 cubic yards, or about 56 bags of 80lb pre-mix (each 80lb bag yields ~0.6 cubic feet).
Formula / Method
Volume (ft³) = Length × Width × Depth (ft)Cubic Yards = Volume (ft³) / 2780lb Bags ≈ Volume (ft³) / 0.6
Worked Example
Example: A 10ft × 10ft slab, 4 inches deep = 100 sq ft × 0.333 ft = 33.3 cubic feet = 1.23 cubic yards, or about 56 bags of 80lb pre-mix (each 80lb bag yields ~0.6 cubic feet).
Formula / Method
Volume (ft³) = Length × Width × Depth (ft)Cubic Yards = Volume (ft³) / 2780lb Bags ≈ Volume (ft³) / 0.6