Concrete Calculator
Use your own numbers after reviewing the formula and worked example.
Quick answer
A continuous rectangular footing is a rectangular prism, so its volume is length × width × depth.
Formula or method
Keep units, percentages and time periods consistent. The formula is useful as a transparent check on the calculator result and helps explain why changing one input changes the answer.
Step-by-step
- Measure footing length.
- Convert width and depth to feet.
- Multiply dimensions to get cubic feet.
- Divide by 27 and add a planning allowance.
Worked example
A 40-foot footing, 16 inches wide and 8 inches deep, is about 35.6 cubic feet or 1.32 cubic yards before waste.
How to interpret the result
Complex foundations may require calculating separate segments and adding their volumes.
When the answer is used for a purchase, loan, payroll decision, construction order, school grade, health estimate or other real-world choice, verify the assumptions that matter in that context. Accurate arithmetic still depends on accurate inputs.
Common mistakes
- Leaving width/depth in inches.
- Forgetting stepped sections.
- Using volume math as a substitute for structural design requirements.
Frequently asked questions
Can the same rectangular formula be used for a footing?
Yes.
How much extra should be ordered?
It depends on project conditions and supplier guidance.
Does the calculator choose footing dimensions?
No.