Concrete Footing Calculator
Calculate the concrete needed for a continuous strip footing.
What you'll need to order
- ready-mix concrete
- rebar
- form lumber
- anchor bolts
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
cubic yards = length × (width ÷ 12) × (depth ÷ 12) ÷ 27
Footings dug rather than formed always take more concrete than calculated, because trench walls slump. Ten percent is a minimum allowance in firm soil and 20% is realistic in loose ground.
Switch the site to metric — the control is in the footer — and your inputs, your results and the tables below follow. The formula, the constants, the guidance text and the sources stay in US units on purpose: that is how the standards they come from are written, and restating them would detach each figure from the document you are meant to be able to check it against.
Where these numbers come from
- ICC International Residential Code 2021, R403.1 — minimum footing widths and depths by soil bearing capacity
Cited to a specific edition on purpose — table numbers and values move between cycles. Confirm against whichever edition is enforced locally.
Worked example
With total footing length 40 ft, footing width 16 in, footing depth 8 in, this calculator returns 1.45 cu yd.
Waste allowance
The headline figure includes a 10% allowance for waste and over-ordering. The exact requirement is shown alongside it.
Concrete for common footing runs
Each row is a link that fills in the calculator above. Send one and the other end sees the same figures you do.
| Job | Size | Concrete to order |
|---|---|---|
| Garage strip footing | 80 ft × 16 in × 8 in | 2.90 cu yd |
| House perimeter | 160 ft × 20 in × 10 in | 9.05 cu yd |
| Shed footing | 40 ft × 12 in × 6 in | 0.81 cu yd |
| Retaining wall base | 40 ft × 24 in × 12 in | 3.26 cu yd |
| Addition footing | 60 ft × 16 in × 8 in | 2.17 cu yd |
Trench walls slump. Ten percent over is a minimum in firm soil; twenty is realistic in loose ground.
Frequently asked questions
How wide should a footing be?
Twice the thickness of the wall it carries, as a rule of thumb — a 8 inch foundation wall wants a 16 inch footing. Poor soil or heavy loads need wider, which is a job for an engineer.
How deep should a footing be?
Below the local frost line, which ranges from nothing in the deep south to 48 inches or more in northern states. The footing itself should be at least 8 inches thick and never thinner than the wall above.
Does a footing need rebar?
Most codes require two continuous #4 bars in a residential strip footing, placed 3 inches up from the bottom and lapped 20 inches at splices. Check locally — some jurisdictions require more.
Why do footings use more concrete than calculated?
Trench walls slump inward and the bottom is rarely flat, so the actual cavity exceeds the nominal dimensions. In loose or sandy soil, budget 20% over the calculated volume.