Ordering and mixing
All-in ballast and cement quantity
- where
- dry volume of materials (m³)
- wet-to-dry volume factor
- volume of concrete needed (m³)
- cement (kg)
- ballast parts per part of cement
- cement bulk density (kg/m³)
- cement bags
- cement bag size (kg)
- all-in ballast (t)
- ballast loose bulk density (kg/m³)
Explain this equation
Works out the cement and all-in ballast for a site mix such as 1:6.
The wet-to-dry factor gives the dry volume for the finished concrete. With 1 part cement to n parts ballast, cement takes 1/(1 + n) of the dry volume and ballast the rest. Bulk densities turn volumes into weights.
Volume shares by ratio, then mass from bulk density.
Sense check: 1 m³ of 1:6 needs about 320 kg of cement (13 bags) and about 2.1 t of ballast.
Watch out: all-in ballast varies a lot in its sand content. For anything structural use a designed mix.
Works out the cement and all-in ballast (combined sand and gravel) for a cement:ballast mix such as 1:6.
Enter your values to see the result.
Good to know
All-in ballast already contains the sand, so a 1:2:4 mix becomes about 1:6 cement to ballast. The same wet-to-dry factor of about 1.54 applies because the dry materials are full of voids. Ballast is usually sold in bulk bags by weight, so the loose bulk density converts volume to tonnes: check your supplier’s figure, as wet ballast is heavier.
Common mistake
Ordering ballast by the bulk bag assuming one bag makes one cubic metre of concrete; it makes noticeably less, because of the voids that the cement and water fill.
Limits
An estimate for volume-batched site mixes. All-in ballast has a variable sand content, so strength is less predictable than with separate sand and coarse aggregate or ready-mix.
Sources
- Brick&Bolt, How many bags of cement for one cubic metre (wet-to-dry factor 1.54; cement 1440 kg/m³; 1:2:4 worked example)
- Calculate.co.nz, Concrete mix ratio calculator (1 m³ wet concrete needs about 1.54 m³ of dry materials; cement about 1440 kg/m³)
- BS 8500-1:2023 Concrete. Complementary British Standard to BS EN 206. Method of specifying and guidance for the specifier
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow BS 8500, BS EN 206, BS EN 752, Building Regulations Part H, manufacturers’ data and your engineer’s design. Structural concrete and foundations need a competent designer.