Calculate concrete, rebar, and formwork needed for strip, pad, or raft foundations.
This foundation calculator estimates the concrete volume for strip, pad or raft foundations (footings), plus a rough guide to rebar and formwork (shuttering). It reports concrete in cubic metres and cubic yards, and in ready-mix or bag terms – in metric or imperial.
| Type | Best for |
|---|---|
| Strip footing | Load-bearing walls |
| Pad footing | Columns / posts / piers |
| Raft / slab | Weak soils, spreading load |
A strip footing 20 m long × 0.6 m wide × 0.25 m deep = 3 m³ of concrete (about 3.9 cubic yards). Add 5–10% waste and order 3.3 m³ of ready-mix.
Strip foundations suit most houses on stable soil. Pad foundations are for point loads like columns. Raft foundations are used on weaker soils to spread the load.
In the UK, minimum depth is typically 1 m below ground. In the US, footings should extend below the frost line, which varies by region.
For foundations, use a minimum C25/30 (GEN 3) mix. For aggressive soil conditions, sulfate-resistant cement may be required.
Strip footings support walls, pad footings support individual columns or posts, and a raft is a single slab spreading the load over the whole footprint.
It depends on the footing dimensions; the calculator multiplies length × width × depth and adds waste to give cubic metres and bags.
