Concrete Footing Calculator — Strip & Pad Footings

Footings spread the weight of a wall, column or deck post into the soil, and they are usually the first concrete poured on a job. This calculator covers the two common kinds: continuous (strip) footings that run under walls, and individual pad footings under posts and piers. Enter the sizes from your plans to get the volume to order, the concrete per foot or per pad, and a premix bag count for small jobs.

How to use this tool

1. Choose US or metric units.
2. Pick continuous footing or pad footings.
3. For a continuous footing, enter the total length along its centre line; for pads, enter how many there are and the pad length.
4. Enter the footing width and depth (thickness) from your drawings.
5. Set the waste allowance — trenches poured without forms usually need more.

Formula

Continuous: V = length × width × depth · Pads: V = number × pad length × pad width × depth

Convert every dimension to the same unit first. Centre-line length works for a uniform closed rectangular strip. At intersections and returns, divide the footprint into non-overlapping rectangles so the same concrete is not counted twice.

Example

A house with 120 ft of continuous footing 20 in wide and 10 in deep holds 120 × 1.667 × 0.833 = 166.7 ft³, or 6.17 yd³; with 10% extra, order 6.79 yd³. Each 10 ft run uses about 0.51 yd³. Eight 24 × 24 × 12 in deck pads need 4 ft³ each, 32 ft³ in total — 1.19 yd³, or 54 bags of 80 lb premix with no waste added.