Calculate the concrete volume and number of bags needed for strip, pad and pier footings.
Footings (called “foundations” in the UK) spread the load of a wall or column onto the ground. Pick the footing type, enter the dimensions, and for pad or pier footings enter how many you are pouring. The tool totals the concrete volume in cubic yards and cubic metres with a waste allowance.
| Type | Shape |
|---|---|
| Strip / trench | Continuous run under a wall |
| Pad | Isolated square base under a post/column |
| Pier | Tall narrow cylinder or square |
A strip footing 30 ft long × 18 in wide × 8 in deep = 30 × 1.5 × 0.667 = 30 ft³ ≈ 1.11 yd³. Four pad footings of 2 ft × 2 ft × 1 ft add 16 ft³ ≈ 0.59 yd³.
Tip: dig footings to firm, undisturbed ground below the frost line (typically 12–24 in / 450–750 mm) and always check the depth required by your local building control or building code.
Roughly 80 bags of 25 kg pre-mixed concrete make up one cubic metre, as each bag yields about 12.5 litres of mixed concrete.
Mixing by hand is fine up to about 0.3–0.5 m³. Above that, ordering a ready-mix truck is usually cheaper and far less work.
Trenches are rarely perfectly even and some concrete is always lost to spillage and over-dig, so 10% is sensible.
Footings should reach undisturbed, firm ground below the frost line — often 450–900 mm in the UK, but always check local building regulations.
A strip footing is typically two to three times the width of the wall it supports; heavily loaded walls need wider footings designed by an engineer.
