Guide
Concrete mix ratios for site-mixed concrete
For general site-mixed concrete, 1 part cement to 5 parts all-in ballast is the common mix, using roughly 15 bags of cement and just over 2 tonnes of ballast per cubic metre; structural concrete should follow the mix your engineer or building control specifies.
Written by the SK Trade team. Last reviewed 1 November 2026.
Common site mixes
| Mix (cement : all-in ballast) | Typical use |
|---|---|
| 1:4 | Stronger general work |
| 1:5 | General purpose: footings for garden walls, bases, posts |
| 1:6 | Blinding and non-structural bases |
Quantities per cubic metre
Dry materials take up more space than the concrete they make, so allow about 1.5 times the finished volume in dry materials. On that basis a cubic metre of 1:5 concrete needs about 370 kg of cement (roughly 15 bags of 25 kg) and about 2.2 tonnes of all-in ballast. Add a little extra for waste and uneven ground.
Designated and structural concrete
Foundations, floor slabs and anything structural are often specified as a designated mix such as GEN1 or RC30/37, or a strength class. Site mixing by hand cannot guarantee those, so for structural work and bigger pours ready-mixed concrete is usually the better route.
When to stop mixing by hand
Hand or mixer batching is fine for small pours. Once you need more than about a cubic metre, the time, labour and consistency usually favour ready-mixed concrete. For a fence post or two, bagged post mix is simplest.
Related products
Related questions
What is all-in ballast?
A mix of sharp sand and gravel up to 20 mm, ready to combine with cement for concrete.
How many bags of cement for 1,000 bricks?
At a 1:4 mortar mix, about 8 to 9 bags of 25 kg cement and roughly 1 tonne of building sand, allowing for waste.
Sources
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