How This Calculator Works
A footing calculator should be more conservative than a surface slab calculator because excavation and soil conditions are less predictable. This concrete footing calculator estimates rectangular footing volume, cubic yards, and bag counts after you know the required footing dimensions.
Formula
Concrete footing volume = length x footing width x footing depth x quantity. Width and depth are entered in inches and converted to feet.
Assumptions
This footing calculator estimates material quantity only. Footing width, depth, reinforcement, and frost depth are design/code questions that must be confirmed separately.
Measurement Checklist
- Use footing dimensions from the plan, engineer, code path, or approved detail before estimating quantity.
- Measure trench width and depth after excavation because soil can slough off and increase volume.
- Calculate repeated pad footings with the quantity field instead of adding rough mental totals.
- Keep reinforcement, forms, gravel, vapor barrier, and inspection requirements outside the concrete volume.
Practical Examples
- A 20 ft strip footing that is 16 inches wide and 12 inches deep needs about 26.7 ft^3 before waste, or 0.99 yd^3. With 10% overage, plan around 1.09 yd^3.
- A footing calculator for a 10 ft trench that is 12 inches wide and 8 inches deep returns about 0.27 yd^3 with 10% overage, or about 13 bags of 80 lb mix.
- A concrete footing calculator for four 2 ft by 24 inch by 12 inch pad footings returns about 0.65 yd^3 with 10% overage, or about 30 bags of 80 lb mix.
- A 40 ft continuous footing that is 18 inches wide and 8 inches deep needs about 1.63 yd^3 with 10% overage, so delivery may be more practical than bags.