Concrete Footing Calculator Formula
Understand the math behind the concrete footing calculator. Each variable explained with a worked example.
Formulas Used
Volume (Cubic Feet)
cubic_feet = length * width_ft * depth_ftVolume (Cubic Yards)
cubic_yards = length * width_ft * depth_ft / 27With 10% Waste
cubic_yards_waste = length * width_ft * depth_ft / 27 * 1.10Variables
| Variable | Description | Default |
|---|---|---|
length | Footing Length(feet) | 50 |
width | Footing Width(inches) | 20 |
depth | Footing Depth(inches) | 8 |
width_ft | Derived value= width / 12 | calculated |
depth_ft | Derived value= depth / 12 | calculated |
How It Works
How to Calculate Concrete for Footings
Formula
Volume = Length (ft) x Width (ft) x Depth (ft)
Convert width and depth from inches to feet by dividing by 12, then divide total cubic feet by 27 for cubic yards. Footings are typically 20 inches wide and 8 inches deep for residential construction, but always follow local building codes.
Worked Example
A continuous footing that is 50 ft long, 20 inches wide, and 8 inches deep.
length = 50width = 20depth = 8
- 01Width in feet: 20 / 12 = 1.667 ft
- 02Depth in feet: 8 / 12 = 0.667 ft
- 03Volume = 50 × 1.667 × 0.667 = 55.56 cu ft
- 04Cubic yards = 55.56 / 27 = 2.06 cu yd
- 05With 10% waste = 2.06 × 1.10 = 2.26 cu yd
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