Concrete & Masonry
Concrete Footing Calculator
Estimate the concrete for continuous wall footings, square pads and round piers. This concrete footing calculator gives the volume of each footing and the total, adds an allowance for uneven trenches, and tells you how much ready-mix to order or how many bags to buy, with an optional cost.
Result
Enter your measurements and press Calculate. What to buy, the working and the cost will appear here.
How to use the concrete footing calculator
- Choose the footing type: a continuous wall footing (a long strip under a wall), a square or rectangular pad, or a round pier.
- Enter the dimensions. For a continuous footing, the length is the total of all runs, usually the perimeter of the foundation.
- Add a row for each kind of footing, and use How many for repeated pads or piers.
- Keep about 10% allowance, since dug trenches are rarely exact, then add prices and press Calculate.
Footing volume formulas
- Continuous footing: total length × width × depth.
- Square or rectangular pad: length × width × depth × number of pads.
- Round pier: 3.1416 × (diameter ÷ 2)² × depth × number of piers.
cubic yards = cubic feet ÷ 27
A 60 ft run of footing 20 in wide and 10 in deep is 60 × 1.667 × 0.833 = 83.3 ft³, or 3.09 cubic yards before the allowance.
Worked example: a garage footing and four pads
A 24 ft × 24 ft garage has a continuous footing around its 96 ft perimeter, 16 inches wide and 8 inches deep, plus four 2 ft × 2 ft pads 12 inches deep for posts. Ready-mix costs $175 a yard:
- Footing 1 – Continuous wall footing: 96 ft × 16 in = 128 ft²; × 8 in deep = 85.33 ft³
- Footing 2 – Square or rectangular pad: 2 ft × 2 ft = 4 ft²; × 12 in deep = 4 ft³ each × 4 = 16 ft³
- Total: 101.33 ft³ = 3.753 yd³
- With allowance: 3.753 yd³ × 1.1 = 4.128 yd³
- Bags: 111.47 ft³ ÷ 0.6 ft³ per bag = 185.78 → buy 186 × 80 lb bags
Order 4.25 yd³ of ready-mix (4.13 yd³ with allowance) for about $743.75. In bags it would be 186 × 80 lb bags, which is why footings are almost always poured from a truck. Open this example in the calculator.
Typical footing dimensions
Footing sizes depend on the load, the soil and your local building code, so they should come from your plans. As a rough guide to what you may see on residential drawings:
| Footing | Often drawn as |
|---|---|
| Continuous footing under a one-story wall | 12–16 in wide, 6–8 in thick |
| Continuous footing under a two-story wall | 15–20 in wide, 7–10 in thick |
| Deck or porch post pad | 16–24 in square, 8–12 in thick |
| Round pier (tube form) | 8–12 in diameter, down to below the frost line |
In cold climates the bottom of every footing must sit below the local frost depth, which can be several feet; that depth is set by your local code.
Pouring footings
- Dig to solid, undisturbed soil and clean loose material out of the trench before the pour.
- Trenches are never exact. Sides slope and corners widen, which is why 10% extra is sensible; for rough digging in rocky soil, use 15%.
- Rebar is usually required in continuous footings; follow your plans. The rebar calculator estimates bar lengths and weight.
- Block walls on top of the footing can be estimated with the concrete block calculator.
Assumptions and limitations
- This estimates concrete quantity only. It does not size footings or check loads, frost depth or soil bearing.
- Footings are treated as regular shapes with straight sides; stepped footings can be entered as separate rows.
- Rebar and anchor bolts take up very little volume and are ignored.
Footing questions
How much concrete do I need for a footing?
Multiply length × width × depth in feet and divide by 27 for cubic yards. A 100 ft footing 16 in wide and 8 in deep is 100 × 1.333 × 0.667 = 88.9 ft³, or 3.29 cubic yards, plus 10% allowance.
How many bags of concrete for a footing pad?
A 2 ft × 2 ft × 12 in pad holds 4 ft³. That is 4 ÷ 0.6 = 6.7, so 7 bags of 80 lb, or 8 with 10% extra; in 60 lb bags it is 9, or 10 with extra.
How deep should a footing be?
Deep enough to reach firm soil and, in cold climates, below the frost line set by your local building code. The footing’s own thickness is often 6–12 in for houses; your plans or building department set the exact figure.
Formulas, unit conversions and default values are explained on our methodology page. Results are estimates; check manufacturer data and local codes before you buy or build.