Concrete Footing Calculator
Calculate the concrete needed for strip, trench and continuous footings.
Enter the total run of the footing along with its width and depth, and get the volume in cubic yards, cubic metres and bags, plus approximate weight and cost.
Measure the total length around the whole perimeter, including any internal load-bearing runs, and enter that as one figure.
How to use the concrete footing calculator
Enter the total footing length around the whole perimeter.
Set the footing width and depth.
Read the volume, bag count and cost.
Why use the Build Tally concrete footing calculator
Perimeter runs
Enter one total length for the entire footing run.
Bag equivalents
See bags needed if you are mixing on site.
Weight estimate
Approximate tonnage for delivery planning.
Metric and imperial
Mix units freely — inches for width, feet for length.
How footings are measured
A footing is a long rectangular prism: total length × width × depth. The width and depth usually come in inches while the length is in feet, which is where errors creep in. A 40 ft run of 16 in wide by 8 in deep footing is 40 × 1.333 × 0.667 = 35.6 cubic feet, or 1.32 cubic yards. When measuring a perimeter, use the centreline of the footing rather than the outside face, or you will over-count the corners.
Footing size is not your choice to make
How wide and how deep a footing needs to be is determined by the load above it, the bearing capacity of your soil and the local frost depth — in cold climates footings must sit below the frost line or they will heave. Those figures come from your building code or an engineer, not from a rule of thumb. This calculator works out how much concrete the dimensions you were given will take.
Trench-fill versus formed footings
Trench-fill footings are poured directly against the excavated earth, which is quick but means the actual volume depends on how neat the excavation is — allow 10% or more on soft or crumbling ground. Formed footings use timber or steel forms and hold their dimensions accurately, so 5% is usually enough.
Read the guide: How Much Concrete Do I Need? A Straight Answer for Slabs, Footings and Posts
Frequently asked questions
How much concrete for a footing?
Multiply total length × width × depth in consistent units, then divide by 27 for cubic yards. Enter your figures above and the calculator handles it.
How deep should a footing be?
Below the local frost line and onto adequate bearing soil. That depth is set by your building code and varies enormously by region — check locally.
How wide should a footing be?
It depends on the load and the soil's bearing capacity. Commonly twice the wall thickness for residential work, but this must be confirmed against your code.
Should I over-order for a trench footing?
Yes — 10% or more. Excavated trench walls are rarely straight and the concrete fills every irregularity.
Do footings need rebar?
Usually yes, and the size and placement are specified by code or by an engineer.
Can I pour footings and slab together?
A monolithic or thickened-edge slab does exactly that. Calculate the footing portion and slab portion separately and add them.
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