Concrete calculator: how many cubic metres?
Add each slab, path, footing and pier and see the cubic metres, the order with waste rounded up, the trucks, the 20 kg bags for a small job and the mesh sheets.
Work out the concrete
No sign-up. Slabs, footings and piers in one order, and nothing is uploaded.
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What it does
- Every pour on one job: slabs, paths and driveways, strip footings and beams, round piers and post holes, and square piers and columns.
- Measured the way you measure: lengths in metres, thicknesses, widths and depths in millimetres, and “how many” for repeats.
- The order, not just the volume: extra for waste, rounded up to 0.1, 0.2 or 0.5 m³, and the trucks it takes.
- Bags and mesh: 20 kg bags for a small pour, and 6 × 2.4 m mesh sheets for the slabs.
- Ready for the quote: copy the order into a quote, a booking or a message, or print it.
How much concrete for a slab
| Slab, 100 mm thick | Concrete | Order with 5% waste | Mesh sheets |
|---|---|---|---|
| 4 × 2.5 m (10 m²) | 1.0 m³ | 1.2 m³ | 1 |
| 5 × 4 m (20 m²) | 2.0 m³ | 2.2 m³ | 2 |
| 6 × 6 m (36 m²) | 3.6 m³ | 3.8 m³ | 3 |
| 10 × 6 m (60 m²) | 6.0 m³ | 6.4 m³ | 5 |
Orders rounded up to the next 0.2 m³. A 125 mm slab needs a quarter more; a 75 mm path a quarter less.
How to use it
- Add each pour: a slab, a footing or piers, with its sizes and how many.
- Set the waste and how the plant rounds orders, and the biggest load a truck carries.
- Check the drawings for thickenings, edge beams and mesh, and add them as their own pours.
- Copy or print the order for the booking and the quote.
Common questions
How much concrete do I need for a slab?
Length × width × thickness in metres. A 6 × 4 m slab 100 mm thick is 6 × 4 × 0.1 = 2.4 m³. With 5% extra for waste it’s 2.52 m³, so order 2.6 m³.
How much concrete for a post hole or pier?
For a round hole, 3.14 × the radius squared × the depth, in metres. A 450 mm hole 900 mm deep holds about 0.14 m³, so four of them need about 0.57 m³.
How many 20 kg bags make a cubic metre?
About 100 to 110 bags, depending on the mix. The calculator uses 0.009 m³ a bag (about 111 bags a cubic metre) to be safe; change it to the yield printed on your bag. Past about half a cubic metre, a truck is usually easier.
How much extra concrete should I order?
Most concreters allow 5 to 10% for uneven ground, formwork bowing and what stays in the truck. Then round up to the plant’s step, usually 0.2 m³, because running short mid-pour is far worse than a little left over.
How many mesh sheets do I need?
A 6 × 2.4 m sheet lapped one 200 mm square each way covers about 12.76 m². A 6 × 4 m slab needs 2 sheets. The engineer’s drawings say which mesh, bar chairs and edge beams the slab needs.
Is anything uploaded?
No. It all runs in your browser, works offline once open, and remembers your last job on your device.
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