Footings Calculator — Continuous Footings by the Run

For foundation footings, stem walls, deck ledgers, and retaining-wall bases. Enter one run's length, the footing width and depth, and how many identical runs you are pouring.

Your footings

Length of one run (feet)

Footing width (inches) Common: 16″ for an 8″ wall, 12″ for light loads.

Footing depth (inches) Common: 8–12″ thick, set below the frost line.

Number of runs A rectangular foundation has 4 runs — or enter the total perimeter as one run.

Waste / overage allowance Always order a little extra. You cannot send back a shortage mid-pour.

Prices — national-average defaults, edit to your local prices

80 lb bag ($)

60 lb bag ($)

50 lb bag ($)

40 lb bag ($)

Ready-mix ($ per cu yd) National average; roughly $140–$170 in most areas.

Delivery fee ($)

Defaults are planning averages, not quotes. Your supplier's prices are the real ones — type them in.

Concrete to order (with your waste allowance)

0 cu yd

80 lb bags

60 lb bags

50 lb bags

40 lb bags

Mix it yourself (bags)

Ready-mix truck

Estimates only, for planning. Footing size and depth are code items — the bottom of the footing must sit below your local frost line, and width depends on soil and load. Confirm with your building department or engineer before you dig.

Worked example: one 40 ft run, 16 inches wide and 8 inches deep: 40 × (16/12) × (8/12) = 35.56 cu ft = 1.32 cu yd. Four runs like that (a 40 × 40 foundation) total 5.27 cu yd — set "number of runs" to 4.

Footing basics worth knowing

Frost line first: the footing's bottom must be below the frost depth for your area — from a few inches in the deep South to 4+ feet up north. Depth in this calculator is the footing's thickness, not the trench depth.
Width spreads the load: a common rule is the footing extends about the wall's thickness on each side. Soft soil needs wider footings.
Undisturbed soil: pour on soil that has not been dug up and refilled loose; if you over-dig, fill the extra with concrete (and count it in your volume) — never with loose dirt.

Frequently asked questions

How deep should a footing be?

Two different numbers: the footing itself is typically 8–12 inches thick, and its bottom must rest below the local frost line. Your trench depth is frost depth plus footing thickness. Frost lines are set by local code — look yours up before digging.

Can I use bags for footings?

For a short run or a couple of deck footings, yes. A house foundation at 5+ cubic yards is truck work — footings need to be poured continuously so they cure as one piece.

Do footings need rebar?

Most codes require continuous horizontal rebar in foundation footings (commonly two #4 bars). This calculator figures concrete volume only; rebar is figured separately by length.