Footing Size Calculator Guide - Width, Depth, Concrete
Use a footing size calculator guide to plan width, depth, length, cubic yards, rebar, excavation, soil, frost, and contractor quote checks.
A footing size calculator can estimate concrete volume from width, depth, and length, but it cannot decide the correct footing size by itself. Soil, load, frost depth, wall type, pier spacing, reinforcement, and code requirements matter before a footing is poured.
Use the Concrete Footing Calculator for volume and the Concrete Footing Calculator Guide for examples. Compare contractor bids in the Concrete Quote Reviewer.
This page adds the size and quote questions that pure volume math can miss: approved width, depth, frost line, soil, rebar, inspection timing, excavation, spoil haul-off, and who owns changes before concrete arrives.
Quick answer
For footing volume:
cubic yards = length ft x width ft x depth ft / 27
Example: a 40 ft continuous footing that is 16 in wide and 8 in deep needs about 1.32 yd3 before waste, or about 1.45 yd3 with 10% waste.
Footing width, depth, bearing, frost, reinforcement, and inspection requirements should be confirmed with a qualified local professional.
Footing size inputs
| Input | Why it matters |
|---|---|
| Total run length | Sets the length of the footing. |
| Width | Affects bearing area and concrete volume. |
| Depth | Affects volume and frost or design requirements. |
| Soil condition | Poor soil may require a different design. |
| Load | Walls, decks, posts, and additions differ. |
| Reinforcement | Rebar size and placement should be written. |
| Excavation | Trench depth and access can drive labor. |
For cost, see Concrete Footing Cost per Linear Foot.
Common footing volume examples
| Footing run | Width x depth | Concrete before waste | With 10% waste |
|---|---|---|---|
| 20 ft | 12 in x 8 in | 0.49 yd3 | 0.54 yd3 |
| 40 ft | 16 in x 8 in | 1.32 yd3 | 1.45 yd3 |
| 60 ft | 18 in x 10 in | 2.78 yd3 | 3.06 yd3 |
| 80 ft | 24 in x 12 in | 5.93 yd3 | 6.52 yd3 |
Use these as volume checks only. They are not footing design recommendations.
Inputs to confirm before sizing the order
Before turning footing size into a concrete order, confirm whether the listed dimensions are finished concrete dimensions or rough excavation dimensions. Plans may show the required footing width and thickness, while the field trench may be wider because of soil conditions, over-excavation, or working room. Using the wrong dimension can under-order concrete or make the estimate look larger than the approved footing actually requires.
Also separate design questions from ordering questions. Bearing capacity, frost depth, wall load, pier spacing, and reinforcement layout belong with the local code official, engineer, or qualified contractor. Once those decisions are known, the calculator can help convert the approved size into cubic yards, bags, ready-mix order volume, rebar scope, inspection timing, and quote questions.
Quote checklist
| Quote line | Confirm |
|---|---|
| Footing dimensions | Width, depth, total run, and sections. |
| Excavation | Spoils, trench depth, access, and cleanup. |
| Rebar | Size, quantity, laps, chairs, and dowels. |
| Inspection | Who schedules and who pays. |
| Concrete order | Yards, delivery, pump, buggy, or wheelbarrow. |
| Exclusions | Rock, water, unsuitable soil, engineering, permits. |
Size vs estimate risk
A footing size calculator is useful after the planned dimensions are known. It is not the tool that should choose dimensions for a structural footing. Treat searches such as "footing size calculator" as two separate jobs: first confirm the required width, depth, frost, soil, load, and reinforcement path; then use the calculator to estimate concrete, delivery, rebar, excavation, inspection, and quote scope.
Sizing handoff for bids
When you send a footing size to a supplier or contractor, include more than the width and depth. Write the total run, number of corners, step-downs, sections with different dimensions, waste factor, ready-mix strength, slump, delivery time, placement method, and inspection requirement. If plans call for different footing sizes in different areas, calculate each section separately and add the totals before waste.
For contractor bids, ask for one line that shows the approved footing size and another line that shows excavation assumptions. A trench can be wider or deeper than the concrete because of soil, access, forms, or cleanup. If the bid does not separate design size from excavation size, you may not know whether the contractor priced the concrete you actually need or the hole they expect to dig. That separation makes change orders easier to question.
Dispatch readiness check
Before ordering, confirm the approved size, total calculated yards, waste, ready-mix minimum, delivery time, and access route with the person responsible for the work. Then confirm forms or trenches are ready, rebar is tied and supported, anchor or dowel locations are known, and inspection is complete if required.
Those items do not change the footing formula, but they decide whether the right amount of concrete can be placed at the right time. A size calculator is most useful when its output becomes a shared checklist for the supplier, contractor, and owner. Keep the checklist with the accepted bid so later quantity, access, and inspection questions can be answered from the same document. If one size changes in the field, update the worksheet and ask whether the order, crew, and inspection timing still match the approved plan. That keeps field changes visible before the truck is scheduled, especially when dispatch windows, rebar layout, or inspector availability are tight.
FAQ
How do I calculate footing concrete?
Multiply footing length by width by depth, keep all dimensions in feet, divide by 27 for cubic yards, then add waste.
Can a calculator choose footing width?
No. A calculator can estimate volume, but footing size depends on loads, soil, frost, code, and structural requirements.
What is the difference between footing size and footing volume?
Footing size is the design dimension. Footing volume is the concrete quantity created by those dimensions.
Should rebar be included in a footing quote?
If reinforcement is required, the quote should state bar size, spacing, laps, dowels, chairs, and inspection responsibility.
When should I get professional help?
Use a qualified local professional for structural loads, retaining walls, additions, poor soils, frost depth, permits, or inspections.
Next step
Calculate volume in the Concrete Footing Calculator, then compare scope in the Concrete Quote Reviewer. Contractors can prepare line items in the Concrete Proposal Kit.
Quote planning next step
Turn this guide into a concrete buying check
Run the matching calculator, then compare ready-mix, bagged concrete, delivery fees, access needs, and quote gaps before you buy materials or approve a contractor number.