DIY Cost Tools
Concrete Footing Calculator
Estimate concrete volume and bag count for a continuous rectangular footing with a waste allowance.
How to use this calculator
- Replace the example values with your own measurements or planning assumptions.
- Keep every value in the unit printed beside its field.
- Select Calculate and review the result together with the formula and limitations below.
Formula and method
Footing volume equals length times width times thickness after converting inches to feet. Apply waste, divide by 27 for cubic yards, and divide by bag yield.
Results are hidden whenever an input changes or validation fails, so an old answer cannot be mistaken for a current calculation.
Worked example
Footing length = 40 ft; Footing width = 1.5 ft; Footing thickness = 8 in; Waste allowance = 10 %; Yield per bag = 0.6 ft³. The calculator returns Concrete required = 44 ft³; Concrete required = 1.63 yd³; Exact bag requirement = 73.333 bags; Whole bags to buy = 74.
The worked example uses the same default values displayed in the calculator.
Limitations and safety
Frequently asked questions
Does this calculator size the footing?
No. Enter dimensions already established by approved plans or a qualified professional; the calculator only estimates concrete quantity.
Why might the real result differ?
This estimates material only and does not design footing dimensions, reinforcement, frost depth, bearing capacity, or code compliance. Obtain qualified structural guidance.
How should I round the answer?
Keep extra precision while planning, then round up when purchasing whole containers, bags, pieces, or stock lengths. Follow the output labels and supplier packaging.
Review notes and reference
Reviewed October 4, 2026. The formula was checked against the displayed worked example, and the script was tested for defaults, boundaries, invalid formats, condition-specific errors, and recovery. Reference: OSHA construction safety resources. Explanations and examples are original.