Concrete Footing Calculator
Choose a strip footing or round pier footings, enter the size and see how much concrete you need in cubic yards, cubic feet and bags. The bag yield is editable.
How to use this concrete footing calculator
- Choose a strip footing for a continuous footing under a wall, or round pier footings for posts and decks.
- For a strip footing, enter the total length in feet and the width and depth in inches.
- For piers, enter the diameter and depth in inches and how many piers you will pour.
- Keep the extra percentage or change it, and check the bag yield against the bag you plan to buy.
- Press Calculate to see cubic yards and bags. Use Copy result or Export CSV.
How to calculate concrete for footings
The calculator finds the volume of the footing and adds an allowance for waste.
- Strip footing = length (ft) x width (ft) x depth (ft)
- Round pier = pi x radius squared x depth, times the number of piers
- Concrete to order = volume x (1 + extra % / 100)
- Cubic yards = cubic feet / 27
- Bags = cubic feet to order / yield per bag, rounded up
Worked example
A strip footing is 40 ft long, 16 inches wide and 8 inches deep. The volume is 40 x 1.333 x 0.667 = 35.56 cubic feet, or 1.32 cubic yards. With 10% extra you need 39.1 cubic feet, or 1.45 cubic yards. With bags that yield 0.6 cubic feet, you need 39.1 / 0.6 = 65.2, so 66 bags.
For six round piers 12 inches wide and 36 inches deep, one pier is pi x 0.5 x 0.5 x 3 = 2.36 cubic feet. Six piers need 14.1 cubic feet, and 0.58 cubic yards with 10% extra.
Assumptions & limits
- The footing is a simple rectangle or cylinder with straight sides. Stepped footings and flared bases need a separate calculation.
- The bag yield is an editable placeholder. Always check the yield printed on the bag of the product you buy.
- The calculator does not choose a footing size or depth. Those depend on the load, the soil, the frost depth and local code.
- Rebar, forms, gravel base and finishing are not included.
- For a large pour, ready-mix delivery is usually priced by the cubic yard, so compare the cubic yard figure with a supplier quote.
Frequently asked questions
How do I calculate concrete for a footing?
Multiply the length, width and depth in feet to get cubic feet, then divide by 27 for cubic yards. Add a little extra for waste.
How do I calculate concrete for a round pier?
Use pi times the radius squared times the depth. A 12 inch pier that is 3 ft deep holds about 2.36 cubic feet.
How many bags of concrete are in a cubic yard?
It depends on the yield of the bag. With a 0.6 cubic foot yield, a cubic yard of 27 cubic feet needs 45 bags.
How deep should a footing be?
It depends on frost depth, soil and local code. Ask your building department. The calculator uses the depth you enter.
Should I add extra concrete?
Yes. Ten percent is a common allowance for uneven digging, spills and forms that bow.
Does it include rebar?
No. Use the Rebar Calculator for the steel, and follow your plans for the layout.
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Last updated: November 2026