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.
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.
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.