Working Out How Much Concrete You Need

The basic formula

Concrete is measured in cubic metres (m³). To calculate the volume you need, multiply the length by the width by the depth of your pour — with all three measurements in metres.

Volume (m³) = Length (m) × Width (m) × Depth (m)

Worked examples

A driveway that's 8m long, 3m wide and 100mm deep: 8 × 3 × 0.1 = 2.4m³ of concrete.

A garage base that's 6m × 6m at 150mm thick: 6 × 6 × 0.15 = 5.4m³.

A foundation trench that's 10m long, 0.6m wide and 1m deep: 10 × 0.6 × 1 = 6m³.

Converting depth from millimetres to metres

Depth is often given in millimetres — 100mm, 150mm, 200mm. To use the formula, divide by 1000 to convert to metres: 100mm = 0.1m, 150mm = 0.15m, 200mm = 0.2m.

How much wastage should I allow?

Ground is rarely perfectly flat and some concrete is lost to spillage and overpour. A 5–10% wastage allowance is sensible for most projects. So if your calculation gives 5m³, order around 5.25–5.5m³.

Because we supply volumetric concrete mixed on site, you only pay for what you pour — so you don't need to round up to a full load and pay for the surplus. Use our concrete calculator to get your estimate, then call us with the figure.