Concrete Volume Calculation: How to Order the Right Amount of Concrete
Published on May 28, 2026 · 10 min read
Concrete is sold by volume, but most builders measure their forms in area or length. Get the conversion wrong and you either pay for an extra truckload you do not need, or you stand in a half-filled form while the mixer drives away. This guide walks through the math the way an experienced foreman thinks about it — by shape, by waste factor, and finally by truck capacity — so the number you call the plant is the number that actually arrives.
The core formula
Concrete volume is always area × thickness, expressed in the same length unit. Keep everything in meters and the answer comes out in cubic meters (m³); keep everything in feet and the answer is in cubic feet, which you then divide by 27 to get cubic yards (yd³). Need to switch between the two later? Use the Volume converter.
Slab on grade
A garage slab measuring 6 m × 7 m poured at 15 cm:
6 × 7 × 0.15 = 6.3 m³. The same slab in feet (≈19.7 × 23 × 0.49) works out to about 222 ft³, or 222 / 27 ≈ 8.2 yd³.
Strip footings
Footings are long, narrow rectangles. Multiply length × width × depth for each run, then sum. For a perimeter of 40 m, footing 0.4 m wide and 0.3 m deep:
40 × 0.4 × 0.3 = 4.8 m³.
Columns and round footings
A circular section uses π × r² × height. For a 0.3 m diameter column 2.7 m tall:
π × 0.15² × 2.7 ≈ 0.191 m³. Multiply by the number of columns. Eight identical columns = 8 × 0.191 ≈ 1.53 m³.
Stairs
Stairs look intimidating but reduce to a triangle plus rectangles. The quick method: treat each step as a rectangular block (tread × riser × width) and add a triangular wedge for the slope beneath. For a flight of 12 steps at 0.28 m tread, 0.17 m riser, 1.0 m wide, the volume is roughly 12 × (0.28 × 0.17 × 1.0) plus the triangular underside — about 0.85 m³. Always round up; stairs notoriously consume more concrete than spreadsheets predict.
The waste factor — never skip it
Theoretical volume is not the volume you order. Forms flex, sub-base is uneven, the truck leaves a film in the drum, and the last wheelbarrow is always half-empty. Add a waste factor on top of your calculated volume:
- Slabs over compacted gravel: +5 to +8%.
- Footings in trenched soil: +10 to +15% (soil collapses inward).
- Stairs and complex formwork: +10%.
- Pumped concrete: +5% extra to account for the line.
So our 6.3 m³ garage slab really needs about 6.6 to 6.8 m³. Round to the nearest 0.25 m³ because that is how the plant delivers — call it 7 m³.
Truck capacity and delivery
A standard mixer truck holds 6–8 m³ (about 8–10 yd³). If your project is just over one truck — say 8.5 m³ — the plant will send one full truck and a second part-loaded truck, and you usually pay a short-load fee on the second one. It is often cheaper to redesign the pour into a single truckload than to pay the surcharge.
Quick reference
| Element | Formula | Typical waste |
|---|---|---|
| Slab | L × W × T | +5–8% |
| Footing | L × W × D | +10–15% |
| Column | π × r² × H | +5% |
| Wall | L × H × T | +5–8% |
| Stairs | steps × tread × riser × W + wedge | +10% |
Three mistakes that cost real money
- Mixing cm and m mid-calculation. A 15-cm slab is 0.15 m, not 15 m. The factor of 100 turns a 6 m³ pour into a 600 m³ disaster on paper.
- Forgetting the sub-base settlement. Loose gravel compresses under wet concrete; an extra centimeter over a 50 m² slab is another 0.5 m³.
- Ordering exactly the calculated volume. A pour that runs short by 0.3 m³ creates a cold joint and a repair bill. The waste factor is insurance, not a tip.
FAQ
How many cubic meters in a cubic yard?
1 yd³ ≈ 0.7646 m³. Equivalently, 1 m³ ≈ 1.308 yd³.
How much does 1 m³ of concrete weigh?
Standard reinforced concrete is about 2,400 kg/m³ — useful for sizing the sub-base and the formwork.
Can I order half a cubic meter?
Most ready-mix plants deliver in 0.25 m³ increments with a minimum of 1 m³, and they will charge a short-load fee below about 4 m³.
Bottom line
Measure in consistent units, multiply area by thickness, add the waste factor, then round up to the nearest 0.25 m³. The cost of an extra quarter-cube is trivial compared to the cost of a cold joint. Crosscheck the result with the ConvertProf Volume converter before you call the plant.