Concrete calculator
A cubic metre of 1:5 concrete takes about 15 bags of cement (25kg) and 2.1 tonnes of ballast.
1:5 mix
- Cement (25kg bags)
- 10
- Ballast
- 1.36 tonnes
- Ballast bulk bags (850kg)
- 2
- Cement
- 244 kg
0.6 m³ of concrete, plus 10% extra, at 100 mm deep.
Estimates for mixing your own. For large pours, ready-mixed concrete is ordered by the cubic metre.
Materials for one cubic metre of concrete
By mix, before any extra for waste.
| Mix | Cement (25kg bags) | Ballast |
|---|---|---|
| 1:4 strong (driveways, garage bases) | 18 | 1.97 t |
| 1:5 general (paths, patios, shed bases) | 15 | 2.05 t |
| 1:6 footings (garden walls, bulk fill) | 13 | 2.11 t |
How we calculate this
We work out the volume of concrete, add extra for waste, then convert it to dry materials. Dry cement and ballast take up more space than the finished concrete, because water fills the gaps between the stones as you mix, so you need about 1.54 times the volume in dry materials.
We split that dry volume by your mix ratio, then convert to weight: cement at 1,440 kg per m³ and ballast at 1,600 kg per m³.
Questions people ask
Which concrete mix should I use?
1:5 cement to ballast suits most garden jobs, such as paths, patios and shed bases. Use a stronger 1:4 for driveways and garage bases, and 1:6 for footings for garden walls. For anything structural on a house, follow your engineer or Building Control.
How much cement and ballast for one cubic metre?
For a 1:5 mix, about 15 bags of cement and 2.1 tonnes of ballast. The table above shows the other mixes.
How thick should a concrete base be?
About 100 mm is common for paths and shed bases on firm ground. Driveways and bases carrying heavy loads are usually thicker, and often sit on a compacted hardcore layer.
Should I mix my own or order ready-mixed?
Mixing your own suits small jobs. For larger pours, ready-mixed concrete delivered by lorry saves a lot of time and gives a consistent mix, and is ordered by the cubic metre.
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