Working out how much concrete you need is straightforward once you know the basic formulas. Concrete is measured in cubic metres (m³). This guide walks you through the calculation for the most common project shapes.
Prefer to skip the maths? Use our free online concrete calculator.
The universal formula
Volume (m³) = Length (m) × Width (m) × Depth (m)
Everything comes down to this. Just measure your area in metres and multiply.
Concrete calculator for a slab
A slab is any flat, rectangular pour — driveways, shed bases, garage floors, patios.
Length × Width × Depth = m³
Example: A driveway 6m long × 3m wide × 0.15m deep:
6 × 3 × 0.15 = 2.7 m³
Typical slab depths:
- Garden shed base: 100mm (0.10m)
- Domestic driveway: 100–150mm (0.10–0.15m)
- Garage floor: 125–150mm (0.125–0.15m)
- Commercial slab / warehouse: 150–250mm (0.15–0.25m)
Concrete calculator for footings
Footings are the concrete strips that support walls and structures.
Length × Width × Depth × Number of runs = m³
Example: Four trench footings each 8m long × 0.6m wide × 0.5m deep:
8 × 0.6 × 0.5 × 4 = 9.6 m³
Concrete calculator for pads
Pad foundations support single columns or posts (fence posts, decking columns, small extensions).
Length × Width × Depth × Number of pads = m³
Example: Ten pads each 0.6m × 0.6m × 0.6m:
0.6 × 0.6 × 0.6 × 10 = 2.16 m³
Concrete calculator for columns
Circular columns use a slightly different formula:
π × (radius)² × height = m³
Example: A column 0.3m diameter (radius 0.15m) and 2.5m tall:
3.14 × 0.15 × 0.15 × 2.5 = 0.177 m³
Do I need extra concrete for wastage?
With traditional ready mix concrete, industry advice is to add 5–10% to your calculated volume to account for:
- Uneven sub-base absorbing some concrete
- Small spillages during placement
- Slight measurement inaccuracies
With volumetric concrete — like the service we run — you never need to add extra. We keep mixing until your pour is done, and you pay only for the exact amount used. No waste, no over-order, no return-load fees.
Skip the maths
Save yourself the calculations — our free concrete calculator handles slabs, footings, pads and columns in seconds. Or get an instant online quote if you’d rather just tell us your dimensions.
FAQs
How do I calculate concrete for a slab?+
Multiply length × width × depth (all in metres). For example a 5m × 3m slab at 0.15m depth = 5 × 3 × 0.15 = 2.25 cubic metres.
How do I calculate concrete for a footing?+
For a rectangular footing: length × width × depth in metres. For a trench footing: length × width × depth, then multiply by the number of trenches.
Should I add extra for wastage?+
With traditional ready mix, add 5–10% to allow for waste. With volumetric concrete (like ours) you only pay for what you actually use — so no extra needed.
What is 1 cubic metre of concrete?+
One cubic metre (m³) is a block of concrete 1 metre long × 1 metre wide × 1 metre deep — roughly 2.4 tonnes.