Free Concrete Footing Calculator
Use this concrete footing calculator to see how much concrete to order for your footing length, width and depth.
A continuous footing is a long strip of concrete that carries a wall. Enter its total length, its width and its depth. For square pier pads, change the quantity to the number of pads.
Footing sizes and how deep they must go below frost level are set by your local building code. Confirm with your building department before you dig.
Concrete footing example
A 40 ft footing, 2 ft wide and 12 in deep: 80 sq ft × 12 in ÷ 12 = 80 cu ft, plus 10% extra = 88 cu ft. Divide by 27 to get 3.26 cubic yards, which weighs about 6.52 tons, or 147 × 80 lb bags (0.60 cu ft).
How deep should concrete be?
| Use | Footing depth | Notes |
|---|---|---|
| Garden wall footing | 8 to 12 in | Width about twice the wall thickness. |
| House or garage wall footing | Set by code | Typically 6 to 12 in thick, below frost depth. |
| Deck pier pad | 8 to 12 in | Use quantity for the number of pads. |
Bags of concrete per cubic yard
| Bag | Yield | Bags per cubic yard |
|---|---|---|
| 40 lb bag | 0.3 cu ft | 90 |
| 60 lb bag | 0.45 cu ft | 60 |
| 80 lb bag | 0.6 cu ft | 45 |
Buying tips
- Measure the actual trench. If it is wider than planned, the concrete fills it all.
- For a footing around a building, the length is the perimeter: add all sides together.
- For round piers or post holes, use the post hole concrete calculator, which handles round holes.
How much does concrete weigh?
A cubic yard of concrete typically weighs 3,800 to 4,200 lb (1.9 to 2.1 tons). The calculator uses 4,000 lb (2 tons) per cubic yard. Moisture and grading change the weight, so if your supplier sells by the ton, ask for their figure.
Frequently asked questions
How much concrete for a 2 ft wide, 1 ft deep footing?
Each running foot needs 2 cu ft. So 40 ft of footing needs 80 cu ft, about 3 cubic yards.
How wide should a footing be?
A common rule of thumb is about twice the width of the wall it supports, but local code decides.
Should I use bags or ready-mix for footings?
Above about 1 cubic yard, ready-mix is usually more practical. Smaller footings for garden walls can be done with bags.
How accurate is this concrete footing calculator?
The concrete footing calculator gives the exact volume for the measurements you enter, then adds 10% extra (you can change it). Weights use a typical 2 tons per cubic yard; real loads vary with moisture, so confirm with your supplier if you buy by the ton. Measure carefully: an error of one inch in depth changes a 3 inch layer by a third.
How the concrete footing calculator works
Volume = area × footing depth. Each area is worked out from its shape (length × width, π × radius², or ½ × base × height), converted to square feet, multiplied by the footing depth in feet, and added up. Cubic feet ÷ 27 = cubic yards.The extra percentage is then added, and bag counts are rounded up to whole bags. See how we calculate for every figure we use.