Concrete Footing Calculator
Continuous strip footings by the linear foot — the yards, the sacks, and the per-foot volume that makes a long run readable.
Concrete Footing Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Straight runs at constant section — steps are segments.
- Neat formed dimensions; earth-cut overpour rides in waste.
- No steel volume deduction (negligible at footing sizes).
In short: A 40 ft wall on a 16 × 8 in footing: 35.56 ft³ net, 1.448560 yd³ ordered with 10% waste — 66 bags or $253.50 of truck. Every linear foot of that strip is 0.888889 ft³ of concrete.
Formula
net ft³ = run × (width ÷ 12) × (depth ÷ 12)
per linear ft = width × depth ÷ 144
order yd³ = net × (1 + waste) ÷ 27
[('run', 'the multiplier that punishes optimism'), ('per foot', "one linear foot's appetite"), ('waste', 'the pour that cannot be short'), ('trench', 'the excavation page owns the digging')]
Worked Example
- Convert width and depth to feet and multiply by the run.
- State the per-linear-foot volume for layout changes.
- Apply waste and convert to yards for the order.
- Price both routes: sacks at the exact yield, truck at the rate.
- Point the trench volumes at the excavation page.
40 ft × 16 in × 8 in: 35.56 ft³ net, 0.888889 ft³ per linear foot, 1.448560 yd³ ordered with 10% waste. That is 66 sacks ($528.00 at $8) or $253.50 of truck at $175 — and 0.888889 yd³ of trench for the excavation page.
Strengths & Limits Of This Model
Where this engine is strong
- Per-linear-foot lens for layout changes
- Trench volume handed explicitly to the excavation page
- Both buy routes priced from the same yards
Where it stops
- Rectangular strips only
- No keyway or step modelling
Practical Use Cases
Wall footings
Continuous strips under bearing walls.
Fence runs
Long, thin pours by the linear foot.
Garden walls
Low strips where the run keeps growing.
Garage entries
Thickened edges priced separately.
Addition planning
Perimeter take-offs before the quote.
Methodology & Editorial Standards
Net volume is run × width/12 × depth/12; the order applies waste and divides by 27. Bag counts ceil at the exact 0.60 ft³ yield and price at the entered sack rate; truck cost is order yards × rate without fees — the concrete page owns the fee fork. Per-linear-foot volume is stated so run changes are one multiplication.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Concrete Footing Calculator — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How do I calculate concrete for a footing?
Run in feet times width times depth in inches, each divided by 12, gives cubic feet; divide by 27 for yards. A 40 ft × 16 in × 8 in strip is 35.56 ft³ = 1.317 yd³ net.
How wide and deep should a footing be?
The folk rule says twice the wall thickness and down to undisturbed or frost-safe soil, but the drawing, the soil and the local code govern. This page prices whatever dimensions you enter and carries no code opinion.
How much waste does a footing need?
At least 10%, more on long runs in soft ground. Footings are the one pour where running short is structural: the new truck must knit into the old pour under the wall, and the joint never fully disappears.
How many bags for a 40 ft footing?
66 of the 80-lb sacks at 16 × 8 in with 10% waste — about $528 of sacks. That is deep in the concrete page's truck territory if a short-load truck can reach the trench.
What is the volume per linear foot for?
Mental math when the layout changes: 16 × 8 in is 0.888889 ft³ per foot, so ten extra feet of wall is 8.89 ft³ — a third of a bag-mix's worth of extra yard you can price in your head.
Does the trench volume match the footing volume?
Only when the footing is formed. Poured against earth, the concrete fills whatever the bucket left — usually a couple of inches wider each side. The excavation page prices that dig; this page prices the neat strip.
Do footings need rebar?
Most residential specs want one or two continuous #4 bars, more on poor soil or heavy loads. Steel does not change the concrete volume — it changes what the footing does when the ground moves.
Can I pour a footing in stages?
Keyed construction joints let you — but each stop is a weak plane under a wall. Better to size the pour so one delivery finishes it; that is why the order is rounded up, never down.
What about stepped footings on a slope?
Break the run into level segments and price each; the per-linear-foot card makes that arithmetic one multiply per segment. The page prices straight runs; steps are several straight runs.
Frost depth and footing depth?
Undisturbed soil below the local frost line is the point of footing depth, and frost lines are map-and-code territory this page deliberately does not guess at. Price the depth you must dig; verify the depth with the authority that inspects it.