Calculate how much hardcore fill you need in tonnes and cubic metres for foundations and sub-bases.
This hardcore calculator works out how much hardcore (crushed brick, concrete or quarried sub-base – called “crushed concrete”, “fill” or “road base” in the US) you need to build up a compacted layer under a slab, driveway or patio. It reports volume in cubic metres and cubic yards plus weight in tonnes, and includes a compaction allowance.
| Use | Imperial | Metric |
|---|---|---|
| Shed / slab base | 4 in | 100 mm |
| Patio / path | 4–6 in | 100–150 mm |
| Driveway (cars) | 6 in | 150 mm |
A shed base 3 m × 3 m at 100 mm = 9 m² × 0.1 m = 0.9 m³. Add 15% for compaction = ~1.04 m³. Hardcore is about 1.9 t/m³, so order roughly 2 tonnes.
Hardcore is crushed brick, concrete or stone used as a compacted base under slabs, driveways, foundations and floors to provide a stable, free-draining layer.
Hardcore weighs roughly 1.9 tonnes per cubic metre, though it varies with the material it is made from.
A typical compacted hardcore layer is 150 mm (6 in) under slabs and driveways. Soft or uneven ground may need more.
Yes — well-compacted hardcore makes a sound sub-base under driveways, but blind it with a layer of MOT Type 1 or sharp sand to give a smooth, level surface before laying paving or concrete.
A bulk bag holds roughly 800 kg and covers about 4–5 m² at 100 mm deep once compacted. For larger areas, ordering loose by the tonne usually works out cheaper.
