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Updated September 2026 · Free reference guideConcrete Calculator Guide: Volume, Depth and Ordering
Concrete quantity is fundamentally a volume calculation. Accurate measurement and a visible ordering allowance are the key planning steps.
Basic concrete volume
Convert length, width and thickness to consistent units, multiply them, then convert cubic feet to cubic yards.
Cubic feet = length (ft) × width (ft) × thickness (ft)
Cubic yards = cubic feet ÷ 27
Cubic yards = cubic feet ÷ 27
If thickness is in inches, divide it by 12 first.
Worked example
Slab: 20 ft × 10 ft × 4 in
Thickness = 4 ÷ 12 = 0.333 ft.
Volume ≈ 20 × 10 × 0.333 = 66.67 ft³.
Volume ≈ 2.47 yd³ before an ordering allowance.
Structural limitation
This is a quantity calculator, not a structural concrete design tool. Strength class, reinforcement, exposure, water-cement ratio, aggregate grading and placement requirements should follow the project specification or qualified professional.