About concrete calculator
Ordering the right amount of concrete avoids waste and delays. The calculator turns slab, footing or column sizes into volume.
Formula
Volume = length × width × thickness. A 10 ft × 10 ft slab 4 inches thick is 10 × 10 × (4 ÷ 12) = 33.3 cubic feet, or about 1.23 cubic yards.
Practical advice
- Add 5 to 10 percent for spillage, uneven ground and over-excavation.
- Check the mix ratio and cement grade with your engineer.
- Always confirm quantities with your contractor before ordering.
A worked example
A slab 4 m × 3 m × 0.1 m is 1.2 m³ of wet concrete. The dry volume is about 1.54 times that, or 1.85 m³. For M20 (1 : 1.5 : 3) the parts add up to 5.5, so the cement is about 0.34 m³, roughly 10 bags of 50 kg, with sand and aggregate in proportion.
Practical points
Order a little extra for uneven ground. Keep the water-cement ratio low for strength, and cure the concrete by keeping it damp for at least seven days.
