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Footing Concrete Calculator
Size your strip or pad footings correctly. Enter length, width and depth: get cubic yards, bags and cost instantly.
Estimates only. Bag yields per manufacturer specs (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³). Ready-mix trucks carry ≈ 10 yd³. Always round up and confirm with your supplier.
Footings spread the load of walls and columns onto the soil. Undersize them and the structure settles. Use the free footing concrete calculator below: enter length, width and depth to get cubic yards, bag counts and cost before you dig.
How to use the footing concrete calculator
- Measure the total length of your footing trench in feet.
- Enter the footing width in feet (2 ft is common for house walls).
- Enter the depth in inches (12 inches is typical).
- Add 10 percent waste for over-dig and uneven trench bottoms.
Formula
Volume = Length × Width × Depth ÷ 27. Convert depth to feet first, then divide cubic feet by 27 for cubic yards.
Practical tips
- Dig footings below the frost line in cold climates, or frost heave will lift them.
- A 20 ft long, 2 ft wide, 12 in deep footing needs 1.48 cubic yards.
- Keep trench bottoms level. Soft spots need compacting before the pour.
- Add rebar lengthwise in structural footings for extra strength.
Frequently asked questions
How wide should a concrete footing be?
For a single-storey wall, 2 ft wide by 12 in deep is standard. Wider footings suit heavier loads or soft soil.
How deep should footings be?
Below the local frost line, with 12 inches as a common minimum for garden walls and extensions.
Can I use bags for footings?
Yes for small runs. A 10 ft footing at 2 ft wide and 12 in deep needs about 34 bags of 80 lb mix. Larger pours suit ready-mix.
Need the full set? Open the concrete calculator hub or estimate rebar for your footings.
Worked examples
Example 1: 20 ft footing, 2 ft wide, 12 in deep. Volume = 20 x 2 x 1 / 27 = 1.48 cubic yards. With 10% waste: 1.63 cubic yards (74 x 80 lb bags).
Example 2: 30 ft footing, 2 ft wide, 12 in deep. Volume = 2.22 cubic yards. With 10% waste: 2.44 cubic yards (110 x 80 lb bags).
Footing concrete reference table
20 ft long footings. Cubic yards before waste; 80 lb bags include 10% waste.
| Footing section | Cubic yards | 80 lb bags |
|---|---|---|
| 20 ft x 1 ft x 12 in | 0.74 | 37 |
| 20 ft x 2 ft x 12 in | 1.48 | 74 |
| 20 ft x 2 ft x 18 in | 2.22 | 110 |
| 20 ft x 3 ft x 12 in | 2.22 | 110 |
More footing questions
How deep should a concrete footing be?
Depth depends on your local frost line and soil. Many footings are 12 inches deep, but in cold climates the base must sit below the frost line. Check local building codes.
How wide should a footing be?
A common rule is twice the width of the wall it supports, but soil bearing capacity governs. When in doubt, ask a structural engineer.
Can I pour a footing with bags?
Yes for small footings. Above about 1 cubic yard, ready-mix is usually worth it.