Concrete Footing Calculator
Works out the concrete for strip footings or pad foundations. Strip footings run continuously under a wall; pads sit under individual columns or posts.
Includes the waste allowance — this is the figure to order.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
volume = length × width × depth × number of footings × (1 + waste)
A footing is a rectangular prism in a trench. The arithmetic is simple; the uncertainty is the trench itself, which is never as neat as the drawing.
What to watch out for
Footings are where over-ordering is cheapest and under-ordering is worst:
- Trenches are never the size you dug them. Sides slump, corners over-dig, and soft spots take more than the drawing says. 10% waste is a minimum here, 15% in anything but firm ground.
- You cannot stop halfway. A footing has to be poured in one go or it needs a proper construction joint. Running out at the last metre is the expensive failure.
- Depth is set by the ground, not the wall. Below frost line, below topsoil, and onto undisturbed bearing soil — which in many places means at least 450–600 mm.
- Pads are counted, strips are measured. Switch the type above and the calculator multiplies or does not.
Frequently Asked Questions
How deep should a footing be?
Deep enough to reach undisturbed load-bearing soil and sit below the frost line. In the UK that is usually 450–600 mm minimum; in cold climates it can be well over a metre. Local building control sets the requirement, not a rule of thumb.
How wide should a strip footing be?
Typically two to three times the wall thickness — 450 mm for a single-skin wall, 600 mm for a cavity wall — but the real answer comes from the soil bearing capacity and the load above.
How much concrete for a 12 m strip footing?
At 600 × 300 mm, a 12 m run is 2.16 m³ before waste — about 2.4 m³ ordered. That is a ready-mix delivery with a short-load fee.
Can I pour footings in sections?
Only with a designed construction joint. An unplanned cold joint in a footing is a weak plane exactly where you least want one.