Quick answer
Concrete Footing Calculator: direct answer
Concrete Footing Calculator helps you estimate concrete volume and bags for continuous footings by length, width, depth, quantity, and waste. It is best for continuous rectangular footings and repeated footing sections and returns cubic feet, cubic yards, whole bag count for material planning.
Use this calculator when you know project shape such as slab, wall, footing, or post hole, length, width, thickness, height, depth, or diameter, quantity when the same shape repeats. The estimate uses this rule: cubic feet = footing length x footing width x footing depth.
Inputs
- Project shape such as slab, wall, footing, or post hole
- Length, width, thickness, height, depth, or diameter
- Quantity when the same shape repeats
- Waste percentage
- Bag size, bag cost, and ready-mix cost when pricing is needed
Outputs
- Cubic feet
- Cubic yards
- Whole bag count
- Estimated material weight
- Estimated material cost
Formula
How this estimate works
cubic feet = footing length x footing width x footing depth
In plain terms, calculate the concrete volume from the shape dimensions, convert cubic feet into cubic yards, then add waste before comparing ready-mix and bagged options.
A 40 ft footing that is 1.5 ft wide and 1 ft deep needs about 2.44 cubic yards with 10% waste.
Use cases
When to use this calculator
Estimate straight wall footings after the required width and depth are known.
Use quantity for repeated piers, pads, or short footing sections with the same dimensions.
Convert trench dimensions to cubic yards before checking supplier minimums and delivery costs.
Worked example
Estimate concrete for a continuous footing
For a simple rectangular footing, the calculator turns length, width, depth, quantity, and waste into cubic yards and bag counts.
- Enter the footing length, width, and depth from the plan or layout.
- Use quantity if several footings share the same dimensions.
- Add waste for trench irregularity, over-digging, and uneven bottoms.
Footing volume calculation
For rectangular footings, multiply length by width by depth to get cubic feet. Divide by 27 to convert the result to cubic yards.
Confirm footing dimensions
Footing width and depth are often governed by structure, soil, frost depth, and local code. Use the calculator after the required dimensions are known.
Measurement tips for a better estimate
- Use the required structural dimensions, not a guess from the trench after soil has sloughed in.
- Measure depth from the bottom of the footing to the intended top of concrete.
- Separate different footing sizes into separate estimates, then add the totals.
Common estimating mistakes
- Treating footing depth like slab thickness and entering inches in a feet field.
- Leaving out repeated footing sections or piers that share the same pour.
- Using the calculator before confirming code, frost depth, soil, and structural requirements.
Assumptions used
- Normal-weight concrete is estimated at 150 lb per cubic foot.
- Premix bag yield is estimated from common 40, 50, 60, and 80 lb bag sizes.
- Waste factor is applied after the base volume is calculated.
Before you order materials
- Confirm footing size from plans or code requirements.
- Use quantity for repeated footings with identical dimensions.
- Estimate reinforcement separately from concrete volume.
Frequently asked questions
Is footing depth the same as slab thickness?
No. Footings use width and depth dimensions, while slabs usually use surface area and thickness.
Does this replace code requirements?
No. It estimates material quantity only. Confirm structural and code requirements separately.
Can I estimate several footings at once?
Yes. Use the quantity field when multiple footings have the same dimensions.