Deck Footing Calculator
Estimate concrete volume, cubic yards, full bags, weight and cost for deck footings. Optionally compare the provided base area with a design reaction and allowable soil pressure supplied by your plans or engineer.
Deck footing formulas
A round pier uses π × diameter² ÷ 4 × depth. Square and rectangular footings use base area × depth. A pad-plus-pier adds the pad prism to the cylindrical pier above it, avoiding overlap.
Total geometric concrete equals one footing volume multiplied by the number of identical footings. The order volume adds the selected allowance. Whole bags are rounded upward using the mixed yield entered from the product label.
Checked example
Six round footings, each 12 in in diameter and 3 ft deep, contain 14.14 ft³ of concrete. With 10% extra, order 15.55 ft³ or 0.576 yd³. At 0.60 ft³ per bag, buy 26 full bags.
If those six footings share a supplied 6,000 lb vertical design reaction and the supplied allowable pressure is 1,500 psf, each footing requires 0.667 ft²: an equivalent 11.06 in round base or 9.80 in square base. A 12 in round base provides 0.785 ft² and uses 84.9% of the supplied arithmetic capacity.
What this calculator includes
| Geometry | Measurements | Bearing base |
|---|---|---|
| Round pier or tube | Diameter and concrete depth | Round bottom area |
| Square footing | Side and depth | Square bottom area |
| Rectangular footing | Width, length and depth | Rectangular bottom area |
| Pad plus round pier | Pad dimensions plus pier diameter and height | Pad bottom area |
Limits and field checks
- Dimensions describe concrete, not excavation clearance, gravel base, forms or disturbed soil.
- Do not substitute generic soil values for a project-specific allowable pressure.
- The group reaction must already include the correct load combinations and load path; the calculator divides it equally among identical footings.
- Unequal tributary areas, beams, cantilevers or concentrated loads require individual reactions rather than equal division.
- Bag yield must come from the actual product. Bag weight alone does not determine mixed volume.
- Ready-mix minimum orders, short-load fees, access, pump, labor, reinforcement, anchors, forms and tax are separate.