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Concrete Footing Calculator

Footings spread the load of walls, posts and columns into the ground. This calculator handles both continuous strip footings (enter the total run) and repeated pad footings (enter the size of one pad and the number of pads).

Enter your measurements

Measurements
ft

For a continuous footing, use the total run (perimeter) of the footing.

in
in
footings

Use 1 for a single continuous footing.

Material & assumptions
%

Covers spillage, uneven subgrade and form movement. 5–10% is a common allowance.

Yields are typical values. Check the yield printed on your product.

Enter your measurements and press Calculate to see quantities, a material breakdown and an optional cost estimate.

How the calculation works

  • Volume per footing = Length × Width × Depth
  • Total volume = Volume per footing × Number of footings × (1 + Waste %)

Footing width and depth are usually specified in inches or centimetres, while length is in feet or metres. The calculator converts everything to a common unit before multiplying.

Assumptions used

  • Footings are rectangular in cross-section with a flat bottom.
  • Reinforcing steel volume is ignored; it displaces a negligible amount of concrete.
  • Footing sizes must follow your local building code or engineer's design. This tool only calculates volume.

Example calculation

A continuous footing 40 ft long, 16 in wide and 8 in deep, with 10% waste.

  1. 1Width: 16 ÷ 12 = 1.333 ft; depth: 8 ÷ 12 = 0.667 ft
  2. 2Volume: 40 × 1.333 × 0.667 = 35.6 ft³
  3. 3Cubic yards: 35.6 ÷ 27 = 1.32 yd³
  4. 4With 10% waste: 1.32 × 1.10 = 1.45 yd³

Result: Order roughly 1.5 yd³ of concrete.

How to measure your project

  • For a perimeter footing, add up all wall lengths. At corners, measure along the outside on two sides and the inside on the other two so overlaps are not counted twice.
  • Measure the trench, not the planned wall: trenches dug wider than the design use more concrete.
  • For square pad footings under deck posts, enter the pad size as length and width, the pad thickness as depth, and the number of pads.

Frequently asked questions

How big should a footing be?

Footing size depends on the load, soil bearing capacity and local code. A common rule for light residential walls is a footing twice as wide as the wall and as deep as the wall is thick, but always check your code or an engineer.

Can I pour footings with bagged concrete?

Yes, for small footings such as deck pads. For long continuous footings, the number of bags quickly becomes impractical and ready-mix is usually better.

Should footings go below the frost line?

In cold climates, codes generally require footings to bear below the local frost depth to prevent frost heave. Your local building department can tell you the required depth.

Related guides

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Results are estimates based on the measurements and assumptions you enter. Always confirm product specifications, local building codes and final quantities with your supplier or a qualified professional. See our disclaimer.