Deck Footing Calculator

The estimate follows six steps:

1. Enter the number of footings from your deck design.
2. Enter the footing shape and its dimensions.
3. The calculator works out the concrete volume of one footing.
4. That volume is multiplied by the footing count.
5. Your selected extra-material allowance is added.
6. The total is converted into concrete bags or bulk volume.

Enter the number of footings specified for your deck design by approved plans, applicable codes, manufacturer guidance or qualified professional advice.

Round footings and form tubes are cylinders, so the volume comes from the radius and the depth:

Volume = π × Radius² × Depth

Total Volume = Volume Per Footing × Number of Footings

You enter the diameter, which is easier to measure, and the radius is calculated as diameter ÷ 2. A 12 in diameter footing 36 in deep works out to about 2.36 ft³, so four of them come to roughly 9.42 ft³ (0.35 yd³) before any allowance.

Square and rectangular footing pads use the same rectangular volume formula:

Volume = Length × Width × Depth

Total Volume = Volume Per Footing × Number of Footings

A square footing uses one side dimension for both length and width. A rectangular footing lets you enter length and width independently. Both run through the same shared engine as the Concrete Footing Calculator, so identical dimensions always produce identical volumes.

Some designs use a wider base footing with a narrower concrete pier above it. BuildCalcWorks can estimate both concrete volumes separately and combine them. BuildCalcWorks does not determine whether a base-plus-pier configuration is appropriate for a deck.

Enter pier height above the top of the base footing. The base and pier volumes are calculated separately and added, so no overlapping concrete is double-counted.

BuildCalcWorks does not determine the required footing size. Footing dimensions depend on factors such as structural loads, soil bearing capacity, local rules, frost conditions and the post and beam layout.

Enter the footing dimensions from your actual project design. Placeholder and example values are input conveniences only — they are not recommended sizes.

The calculator does not determine local frost depth or a minimum footing depth. Those requirements vary by location and project.

No universal depth is provided here. Use the depth specified by your plans, applicable local rules or a qualified professional, then enter it to calculate concrete volume.

Concrete quantity can be calculated from the dimensions you enter, but BuildCalcWorks does not determine the required footing area from soil bearing capacity.

Sizing a footing to the soil beneath it is a structural and design consideration that sits outside this calculator.

This calculator does not determine a structural footing count. You enter the footing count specified for your deck design.

If you are planning materials from a post layout you already have, the Decking Calculator can pass its footing count into this page so you do not have to retype it.

Bags = Recommended Concrete Volume ÷ Yield Per Bag

Bags = recommended concrete volume ÷ yield per bag, always rounded up to whole bags. Concrete mix yields vary by product. Use the yield printed on the bag when available.

For 10 ft³ of recommended concrete and a bag that yields 0.6 ft³, 10 ÷ 0.6 = 16.7, so 17 bags. Bag counts here match the Concrete Bag Calculator for the same volume and yield.

Smaller projects may use bagged concrete mixed on site. Larger quantities may be purchased as ready-mix or bulk concrete.

Volume and bag quantities are both reported. BuildCalcWorks does not recommend a purchasing or delivery method.

Actual holes and forms can differ from the entered dimensions because of excavation irregularities, loose soil, spillage and measurement differences.

Extra material can help account for excavation variation, spills and measurement differences. BuildCalcWorks does not determine a required allowance for your project. Calculated concrete volume is the geometric volume of the entered footings. Recommended order volume adds your selected extra-material allowance on top of it.

Optional. Many deck footings use post bases rather than posts embedded directly in concrete. When enabled, the embedded post volume is subtracted using the same shared logic as the Post Hole Concrete Calculator.

Concrete Volume = Footing Volume − Embedded Post Volume

Enter actual post dimensions rather than nominal sizes. If the entered post volume equals or exceeds the footing volume, the calculator flags it instead of returning a result.

Cost is optional and uses prices you enter — per bag, per cubic yard or per cubic meter, one method at a time. A fixed delivery or freight amount can be added.

Concrete material estimate only. Excavation labor, forms, rebar, anchors, post bases, permits, inspection and equipment are not included.

Use the full Decking Calculator to estimate deck boards, joists, posts, footings, concrete, fascia and fasteners.

Joist quantity and layout are separate calculations. A joist layout does not determine footing sizing here.

How BuildCalcWorks calculations are created →