About

For many domestic projects like fence posts, garden paths, or shed bases, buying separate sand and stone is inefficient. "Builder's Ballast" (or All-in-Aggregate) is a pre-mixed blend of sharp sand and 20mm gravel. This calculator simplifies the mix design to just two components: Ballast and Cement.

While convenient, Ballast varies in density depending on moisture content. This tool uses a standard bulk density average of 1750 kg/m³ to ensure you order enough material, preventing the common issue of running short halfway through a pour.

Formulas

The calculator assumes a bulking factor for the wet mix. To produce 1 m³ of wet concrete, you typically need approximately 1.5 m³ of dry uncompacted materials.

M_ballast = V_conc × 1.2 × 1800

This ensures the voids in the gravel are filled with the sand-cement paste without losing final volume.

Reference Data

Mix Ratio (Vol)	Application	Cement Bags per m³	Ballast Weight per m³
1 : 4	Driveways / Garage Floors	13 bags	1750 kg
1 : 5	Pathways / Patios	11 bags	1800 kg
1 : 6	Foundations / Footings	9 bags	1850 kg
1 : 8	Lean Mix / Kerb Backing	7 bags	1900 kg

Frequently Asked Questions

Ballast is a mix of sand and gravel used for making concrete (by adding cement). MOT Type 1 is crushed stone used for sub-bases (hardcore) under the concrete. You cannot make good concrete with MOT Type 1 as it contains too many fines and clay.

Yes, this is the most common method. The ratios (e.g., 1:5) refer to volume. So, 1 shovel of cement to 5 shovels of ballast. Ensure the shovel sizes are consistent.

Water is not a dry input, but it is critical. For ballast mixes, add water slowly until the mix is workable. Ballast is often stored outside and may already be wet, so water requirements vary drastically.