Concrete footing calculator
Footings are long and narrow, so the volume is small but the ordering error is easy to make.
%
Concrete to order
3.960m³
- Net volume
- 3.600
- In cubic yards
- 5.179
- 25 kg bags
- 360
- Weight
- 9504
- Spoil to remove, loosened
- 4.950
Show the working
- Footing type = 1
- Length of the run, or pad length = 20
- Width = 0.6
- Depth = 0.3
- Number of pads = 8
- Waste allowance = 10
- unit_volume = 20 * 0.6 * 0.3 = 3.6
- Net volume = 1 > 0 ? 3.6 : 3.6 * 8 = 3.6
- Concrete to order = 3.6 * (1 + 10/100) = 3.96
- Weight = 3.96 * 2400 = 9504
- In cubic yards = 3.96 / 0.764554857984 = 5.179 48
- 25 kg bags = ceil(3.96 / 0.011) = 360
- Spoil to remove, loosened = 3.96 * 1.25 = 4.95
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- strip: volume = length x width x depth
- pads: volume = length x width x depth x count
Excavated soil bulks up by 20 to 30% when loosened, which is what the spoil figure allows for.