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Footing Dimension Configurator
Configure geometry and material constraints
How to Calculate Concrete for Footings: A Simple Guide
Planning a new deck, fence, or home addition? The most important step is getting your foundation right. That means knowing exactly how much concrete to order for your footings so you don’t run out mid-pour or waste money on extra materials.
What is a Concrete Footing?
A footing is the very bottom part of a foundation. It is poured underground to support the weight of a structure and keep it from sinking into the soil. Depending on your project, you will usually use one of three shapes:
- Strip Footings: Long, continuous lines of concrete used under foundation walls.
- Pad Footings: Square or rectangular blocks used under heavy columns or posts.
- Round Piers: Cylindrical holes (often using cardboard Sonotubes) used for decks and fences.
The Easy Footing Math Formula
Our calculator does the hard work for you, but it helps to know how the math works. Concrete is always measured and ordered in Cubic Yards.
For Square/Rectangle Footings:
Volume = Length × Width × Thickness (all in feet) ÷ 27
Because you usually measure width and thickness in inches, you must divide those numbers by 12 to turn them into feet before multiplying them together!
Pro-Tips for Your Footing Project
- Always Add 10% Extra: Holes dug in dirt are never perfectly straight. Dirt soaks up moisture, and spillage happens. Adding a 10% waste buffer ensures you don’t run short.
- Dig Below the Frost Line: In cold climates, water in the ground freezes and expands. If your footing isn’t dug deeper than your local frost line, the freezing ground can push your entire structure upward. Check your local building codes for the exact depth required.
- Bags vs. Ready-Mix Truck: If your project requires more than 1 Cubic Yard of concrete, mixing it by hand with 80lb bags will take a long time (about 45 bags per yard!). For anything over 1 or 2 yards, it is usually much faster to call a local ready-mix concrete truck delivery.
Frequently Asked Questions
Question: How many 80lb bags of concrete make a cubic yard?
Answer: It takes exactly 45 bags of 80lb concrete mix to fill one cubic yard. One single 80lb bag yields about 0.60 cubic feet of wet concrete.
Question: What is the minimum thickness for a concrete footing?
Answer: According to standard residential building codes (like ACI 318), a concrete footing should have a minimum thickness of 6 inches to safely spread structural weight across the soil.
Question: How long should a concrete footing cure before building on it?
Answer: While concrete takes 28 days to reach its full design strength, you can generally begin framing light wood structures (like a deck) on your footings after 24 to 48 hours of curing time.
