Ordering the right amount of concrete matters. Order too little and your crew may have to stop mid-pour, leaving a weak joint. Order far too much and you pay for concrete you can’t use. The good news: the calculation is simple once you know the formulas.
Start with the units
Ready-mix concrete is ordered in cubic metres (m³). One cubic metre is a cube 1 m × 1 m × 1 m, equal to 1,000 litres or about 35.3 cubic feet.
Always convert every measurement to metres before you multiply. A 125 mm slab is 0.125 m thick; a 230 mm column is 0.23 m wide.
The formulas
- Slab, footing or beam: Length × Width × Thickness (or depth) × Number of identical elements
- Rectangular column: Width × Depth × Height × Number of columns
- Round column: 3.1416 × (Diameter ÷ 2)² × Height × Number of columns
Worked examples
A house slab
A slab 10 m long, 8 m wide and 125 mm thick:
10 × 8 × 0.125 = 10 m³
Isolated footings
Twelve footings, each 1.2 m × 1.2 m × 0.45 m deep:
1.2 × 1.2 × 0.45 = 0.648 m³ each
0.648 × 12 = 7.78 m³
Columns
Twelve columns, each 230 mm × 300 mm and 3 m high:
0.23 × 0.30 × 3 = 0.207 m³ each
0.207 × 12 = 2.48 m³
Prefer not to do the maths? Use our concrete quantity calculator →
Add a wastage allowance
Real sites are never perfectly level. Formwork deflects slightly, some concrete is lost in spillage, and pumping lines need concrete to prime them. It’s usual to add a small allowance, often 3% to 5%, and sometimes more on uneven ground or long pump lines.
For the 10 m³ slab above, a 5% allowance gives 10 × 1.05 = 10.5 m³.
Things that change the quantity
- Drops and thickenings: beams cast with the slab, sunken areas for toilets, or thicker edges add volume.
- Openings: staircase or duct openings can be subtracted.
- Uneven bases: excavations for footings are rarely exactly to size; measure the actual pit if you can.
Your engineer or contractor can confirm quantities from the drawings, which is always the most reliable source.
Rounding up your order
Ready-mix is ordered in practical steps, and running short mid-pour is much worse than having a small amount left over. If your calculation lands between steps, round up. Our team will help you choose a sensible quantity and plan the loads so concrete arrives steadily.
Key takeaways
- Convert all dimensions to metres before multiplying.
- Volume = Length × Width × Thickness × Quantity; round columns use 3.1416 × r² × Height.
- Add a 3–5% wastage allowance, more for difficult sites.
- Confirm quantities with your engineer and round up rather than down.
Frequently asked questions
How many cubic feet are in one cubic metre?
About 35.3 cubic feet.
Should I include beams in my slab quantity?
Yes, if they’re cast together with the slab. Calculate the part of each beam below the slab separately and add it to the slab volume.
Why does the pump need extra concrete?
The pump line holds concrete that can’t all be placed, and the line is primed at the start. Tell us if you’re using a pump so we can allow for it.
