Concrete Footing Calculator
Enter the footing dimensions from your plans — length, width, depth, and how many — and get the exact pour volume in cubic feet and yards plus bag counts from manufacturer yield data. This tool computes volume for dimensions you already have; it never sizes a footing, because footing sizing is structural, code-governed engineering.
Footing dimensions (from your plans)
Example: two 20 ft × 16 in × 8 in footings at 10% waste → 1.32 cu yd, 66 bags of 80 lb mix.
Structural boundary: footing sizing — width, depth, frost embedment, reinforcement, soil bearing — is engineering governed by your building code. Take the dimensions from your approved plans or engineer; this tool only totals the concrete they require.
Exact geometry, then bags
The worked example: each 20 ft × 16 in × 8 in footing is 20 × (16 ÷ 12) × (8 ÷ 12) = 17.78 cu ft. Two of them total 35.56 cu ft = 1.32 cu yd. Adding the 10% pour allowance gives 39.11 cu ft to mix — 66 bags of 80 lb mix at the manufacturer's 0.60 cu ft yield. Every figure above is computed at build time by the same engine wired to the form.
What is sourced, what is yours
The only external constants on this page are the bag yields, taken from the QUIKRETE Concrete Mix No. 1101 data sheet (and the Canadian manufacturer's figures for metric bags) and locked by automated tests. Everything else — dimensions, count, waste, price — is yours. The calculator never suggests a footing size, a mix strength, or a rebar layout: those come from plans and code.
The rest of the pour
Round piers or formed columns on top of the footing? The concrete column calculator handles cylinders and rectangular forms. Setting posts instead of pouring strip footings is the post hole calculator's job, slab-on-grade volume is the concrete slab calculator's, and to compare every bag size for an arbitrary volume there is the concrete bag calculator. Reinforcement counts for the slab above the footing live in the rebar calculator.
Frequently asked questions
Does this calculator tell me how big my footing should be?
No — deliberately. Footing width, depth, frost embedment, and reinforcement are structural, code-governed design decisions that depend on soil bearing, loads, and your local frost line. Those dimensions come from your plans, your engineer, or your building department; this tool only converts dimensions you already have into a concrete volume and bag count.
How is the volume computed?
Pure geometry: length in feet × width and depth converted from inches to feet, times the number of identical footings. Two 20 ft × 16 in × 8 in footings are 20 × 1.333 × 0.667 = 17.78 cu ft each, 35.56 cu ft total — about 1.32 cubic yards. Nothing is rounded until the final ceil to whole bags.
Where do the bag yields come from?
The QUIKRETE Concrete Mix (No. 1101) product data sheet: 0.30, 0.375, 0.45, and 0.60 cu ft per 40, 50, 60, and 80 lb bag, or the manufacturer-stated 0.43 and 0.52 cu ft for the metric 25 and 30 kg bags sold in Canada. Other brands are batched similarly, but check your bag if you buy a different product.
When should I order ready-mix instead of bags?
A common rule of thumb is around a cubic yard: continuous footings for even a modest addition quickly pass the point where mixing 60+ bags by hand makes sense. For larger pours, take the cubic-yard figure from this page to the concrete slab calculator’s quarter-yard ordering logic, or straight to your ready-mix supplier.
Why is waste added before rounding to bags?
The waste percentage (default 10%, the common convention for concrete pours — spillage, uneven trench bottoms, over-excavation) is applied to the volume first, and only then is the result rounded up to whole bags. Padding whole bags after rounding would count the margin twice.
Dimensions never leave your browser. Bag-yield sources and the estimating pipeline are documented on the methodology page.