Estimate the volume of concrete a slab, path or footing needs, in cubic meters, cubic feet and cubic yards.
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A 5 × 3 m patio slab 0.1 m thick needs 1.5 m³, and a 4 × 4 m slab 15 cm thick needs 2.4 m³. In imperial mode a 10 × 10 ft slab 4 inches thick is 33.33 ft³, about 1.23 cubic yards.
Volume is length × width × depth. In metric mode all three are meters, so convert centimeters first. In imperial mode length and width are feet while depth is inches, because slab thickness is usually quoted that way, and the result is shown in all three volume units.
The figure is the exact geometric volume with no allowance added. Uneven ground, forms that bow, spillage and the concrete left in the truck or mixer mean you should normally add around 5–10%, more for irregular excavations. The tool does not choose thickness, reinforcement, sub-base or concrete strength.
In metric mode, enter length, width and depth in meters. A 5 × 3 m patio slab 0.1 m (10 cm) thick needs 1.5 m³, and a 4 × 4 m slab 15 cm thick needs 2.4 m³. In imperial mode, length and width are in feet and depth is in inches, because slab thickness is usually quoted that way: a 10 × 10 ft slab 4 inches thick is 33.33 ft³, or about 1.23 cubic yards. Always convert centimeters to meters before entering a metric depth.
The same length × width × depth calculation works for strip footings and paths. A footing 10 m long, 0.4 m wide and 0.3 m deep needs 1.2 m³. Ready-mix suppliers in the United States sell by the cubic yard, so a 20 × 12 ft slab at 4 inches, which is 80 ft³ or about 2.96 yd³, would usually be ordered as at least 3 yards plus waste. Thickening the same kind of slab to 6 inches increases volume by half: a 12 × 12 ft slab at 6 inches is 72 ft³, about 2.67 yd³.
The result is the exact geometric volume. Uneven ground, forms that bow, spillage and the concrete left in the truck or mixer mean you should normally add around 5–10%, more for irregular excavations. For bagged mix, divide the cubic feet by the yield printed on the bag; many 80 lb bags yield about 0.60 ft³, so 33.33 ft³ needs roughly 56 bags before waste. The calculator does not choose thickness, reinforcement, sub-base or concrete strength, which depend on loads, soil and local building codes.
| Input | Result |
|---|---|
5 × 3 × 0.1 m | 1.5 m³ · 1.96 yd³ |
4 × 4 × 0.15 m | 2.4 m³ · 3.14 yd³ |
10 × 0.4 × 0.3 m | 1.2 m³ · 1.57 yd³ |
10 ft × 10 ft × 4 in | 33.33 ft³ · 1.23 yd³ |
20 ft × 12 ft × 4 in | 80 ft³ · 2.96 yd³ |
12 ft × 12 ft × 6 in | 72 ft³ · 2.67 yd³ |
Usually 5–10% above the calculated volume, and more when the excavation is irregular. Ready-mix in the United States is sold by the cubic yard, so a 20 × 12 ft slab at 4 inches, which is 80 ft³ or about 2.96 yd³, is normally ordered as at least 3 yards plus waste.
Divide the cubic feet by the yield printed on the bag. Many 80 lb bags yield about 0.60 ft³, so 33.33 ft³ needs roughly 56 bags before waste. Bag yields differ by product and country, so check the label rather than reusing this figure.
Yes, the same length × width × depth calculation applies to strip footings and paths. A footing 10 m long, 0.4 m wide and 0.3 m deep needs 1.2 m³. Thickness changes volume proportionally: a 12 × 12 ft slab at 6 inches is 72 ft³, about 2.67 yd³, half as much again as the same slab at 4 inches.