Concrete Calculator
Calculate how much concrete you need for slabs, walls, footings and round columns, in cubic meters, cubic yards or bags.
Inputs
5–10% is common
Printed on the bag, e.g. 17 L
Result
Concrete needed
1.32m³
1.73 yd³
- In liters
- 1,320L
- Volume per piece (no waste)
- 1.2m³
Formula
Volume = Length × Width × Thickness × Quantity × (1 + Waste)
How it works
Concrete is ordered by volume. The calculator works out the volume of a slab, wall or footing (length × width × thickness) or of round columns (π × radius² × height), multiplies it by the quantity and adds a waste allowance.
- Each dimension has its own unit, so you can enter the slab in meters or feet and the thickness in centimeters or inches.
- Results are shown in cubic meters and cubic yards, the units ready-mix suppliers use.
- For bagged premix, enter the yield printed on the bag to get the number of bags.
Add 5–10% for spillage, uneven ground and over-excavation. Round up when ordering ready-mix — running short mid-pour is far more expensive than a little extra.
Formula
- Slab, wall or footing: V = Length × Width × Thickness
- Round column: V = π × (D ÷ 2)² × Height
- Total = V × Quantity × (1 + Waste ÷ 100)
- 1 yd³ = 0.764555 m³ · 1 m³ = 1,000 L
Example
A 4 × 3 m slab, 10 cm thick, 10% waste
- 14 m × 3 m × 0.10 m = 1.2 m³
- 21.2 m³ × 1.10 = 1.32 m³
- 31.32 m³ ÷ 0.764555 = 1.73 yd³
Order 1.32 m³ (1.73 yd³) of concrete.
Frequently asked questions
How thick should a concrete slab be?
Patios and walkways are commonly 10 cm (4 in), driveways 10–15 cm (4–6 in). Follow local building codes and your engineer's specification for structural slabs.
How many bags of concrete do I need?
Divide the volume by the yield printed on the bag. In the US, an 80 lb bag of premix typically yields about 0.6 ft³, so a cubic yard needs roughly 45 bags.
Should I order extra concrete?
Yes. Add 5–10% to cover uneven subgrade, form movement and spillage.