Why cubic metres matter
Concrete is priced and delivered by the cubic metre (m³), so getting the volume right is the difference between ordering enough and running short mid-pour. The calculation itself is straightforward — the mistakes people make are usually in unit conversions and forgetting the wastage allowance.
If you can measure your pour area in metres and convert the depth from millimetres, you can calculate concrete volume accurately enough to order with confidence.
The formula for rectangular pours
For a rectangular slab, trench or base: Volume (m³) = Length (m) × Width (m) × Depth (m). A driveway 8m × 3m at 100mm deep is 8 × 3 × 0.1 = 2.4m³.
Depth in millimetres must be converted to metres first — divide by 1000. So 150mm = 0.15m and 200mm = 0.2m. This is the most common source of errors.
Circular and irregular shapes
For a circular pad or column: Volume = π × radius² × depth. A pad 1.2m across (radius 0.6m) at 150mm deep is 3.14 × 0.36 × 0.15 = 0.17m³.
For irregular shapes, break the area into rectangles and circles, calculate each separately, and add them together. Our concrete calculator handles the common shapes for you.
Allow for wastage
Ground is rarely perfectly level and some concrete is always lost in the chute, pump or barrow. Add 5–10% to your calculated volume. If you calculate 5m³, order 5.25–5.5m³.
With volumetric concrete, you only pay for what you pour — so you don't need to round up to a full load. Use our concrete calculator, then call us with the figure.
Related services
Need concrete for your project? We supply volumetric concrete across South Wales, mixed fresh on site to the exact quantity you need. Request a quote or call 01495 820164.