Concrete Footing Calculator
Calculate ready-mix yards and common bag quantities for one continuous footing or several equal rectangular footings.
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How this calculator works
Base cubic feet = length × (width ÷ 12) × (depth ÷ 12) × quantity. The extra-material percentage is added, then cubic feet are divided by 27 for cubic yards. Bag alternatives use approximate yields of 0.45 cubic feet for a 60-pound bag and 0.60 cubic feet for an 80-pound bag.
Worked example
One footing that is 20 feet long, 16 inches wide, and 8 inches deep has a base volume of about 17.78 cubic feet. With 10% extra, the order-ready estimate is about 0.72 cubic yard, 44 60-pound bags, or 33 80-pound bags.
Sources & assumptions
Volume uses rectangular-prism geometry and standard unit conversion. Bag yields follow QUIKRETE Concrete Mix product data. Confirm ready-mix order increments and minimums with the supplier.
Frequently asked questions
Does this calculator choose the footing size?
No. It only calculates volume from the dimensions entered. Loads, soil, frost, reinforcement, and local code determine the required design.
Can I use it for isolated pads?
Yes, when the pads are rectangular and equal in size. Enter one pad’s length, width, and depth, then use the quantity field.
Why include extra concrete?
Excavation and forms are rarely perfect. A deliberate allowance helps account for variation, spillage, and small measurement errors.