Concrete Volume Calculator
Calculate concrete in cubic yards and meters for slabs, footings, columns, and steps.
Returns bag count or ready-mix loads with 10% waste allowance.
Concrete volume calculation determines how much ready-mix or bagged concrete is needed for a pour. Ordering too little causes cold joints (structural weakness); ordering too much wastes money. Always include a 5–10% overage buffer.
Volume formulas by shape:
Rectangular slab: Volume (ft³) = Length × Width × Thickness Convert to cubic yards: Volume (yd³) = Volume (ft³) / 27
Circular slab (patio, column footing): Volume = π × Radius² × Thickness
Cylindrical post or tube form: Volume = π × (Diameter/2)² × Height
Trapezoidal footing (wider at base): Volume = Thickness × (Top Width + Bottom Width) / 2 × Length
Unit conversions:
- 1 cubic yard = 27 cubic feet = 0.7646 cubic meters
- 1 cubic meter = 1.308 cubic yards
Bagged concrete yield:
| Bag Size | Yield |
|---|---|
| 40 lb bag | 0.30 ft³ |
| 60 lb bag | 0.45 ft³ |
| 80 lb bag | 0.60 ft³ |
Ready-mix ordering: Sold by the cubic yard. Minimum orders typically 1 yard. Delivery trucks carry 8–10 yards.
Worked example: A 12 ft × 20 ft concrete patio, 4 inches (0.333 ft) thick: Volume = 12 × 20 × 0.333 = 79.92 ft³ In cubic yards = 79.92 / 27 = 2.96 yd³ With 8% overage = 2.96 × 1.08 = 3.20 yd³ → order 3.5 yards
Using 80 lb bags: 79.92 / 0.60 = 133 bags (without overage) With 8% buffer: 144 bags — and at $8/bag, that’s $1,152 vs. ready-mix at ~$200/yd³ × 3.5 = $700.
Ready-mix is cheaper at scale. Bags make sense for volumes under 1 cubic yard or remote locations without truck access.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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