Concrete Footing Calculation Examples for Walls, Decks, and Garages
Learn how to estimate concrete for continuous footings with formulas, strip footing, wall, deck, garage, trench, waste factor, bag counts, ready-mix cost, inspection, and quote checks.
Footing estimates are usually simple in shape but important in planning. A long continuous footing can add up quickly, and small measurement changes can affect the concrete order.
Use these examples to understand the math, then use the Concrete Footing Calculator to estimate cubic yards, bags, waste, and material-only cost.
For the full estimating workflow, see the Concrete Footing Calculator Guide. For round post holes or pier holes, see the Concrete Post Hole Calculator.
Quick answer
For a continuous rectangular footing, multiply length by width by depth, convert to cubic yards, then add waste. A 40 ft footing that is 16 in wide and 8 in deep needs about 1.32 yd3 before waste, or 1.45 yd3 with a 10% waste factor.
That number is a material estimate, not footing design approval. Footing size, depth, reinforcement, frost depth, bearing soil, inspection, and code requirements should come from the approved plan or a qualified professional.
Continuous footing formula
For a rectangular continuous footing:
cubic feet = length ft x width ft x depth ft
cubic yards = cubic feet / 27
If width and depth are measured in inches:
cubic yards = length ft x width in x depth in / 144 / 27
Then add waste:
order quantity = cubic yards x (1 + waste percentage)
If a project has multiple footing runs, calculate each run or group separately, add the base volumes, then apply waste before pricing.
Best calculator inputs for footing examples
Use the calculator with the dimensions that will actually be poured. Footing examples are useful for learning the math, but real projects often have separate runs, different widths, over-dug trenches, inspection timing, and reinforcement details.
| Input | Good planning default | When to change it |
|---|---|---|
| Run length | Use each continuous footing run or a grouped total. | Separate sides, interior runs, thickened sections, and changed widths. |
| Width and depth | Use approved plan dimensions for early planning. | Recheck with actual trench dimensions after excavation. |
| Number of runs | Group identical runs together. | Split runs when width, depth, reinforcement, or inspection sequence differs. |
| Waste factor | 10% for early planning. | Increase for rough excavation, cave-ins, water, soft soil, or hand cleanup. |
| Price per yard | Use a local ready-mix quote. | Replace it when mix strength, short-load fee, pump, buggy, tax, or wait time changes. |
| Pour method | Start with truck chute if access is simple. | Add pump, buggy, wheelbarrow, or crew time when access is limited. |
Run one estimate from the approved dimensions, then run a second check after the trench is cleaned and inspected. The second number is the one that helps avoid short ordering before the truck arrives.
Common footing examples
These examples use 10% waste. They are material planning numbers, not structural specifications.
| Footing example | Size | Base volume | With 10% waste |
|---|---|---|---|
| Small wall run | 40 ft, 16 in x 8 in | 1.32 yd3 | 1.45 yd3 |
| Two garage runs | 2 x 24 ft, 18 in x 10 in | 2.22 yd3 | 2.44 yd3 |
| Garage perimeter | 84 ft, 18 in x 10 in | 3.89 yd3 | 4.28 yd3 |
| Larger wall run | 100 ft, 24 in x 12 in | 7.41 yd3 | 8.15 yd3 |
Bag and delivery checks:
- 40 ft wall run: about 66 80 lb bags, or about $364.25 at $165/yd3 plus a $125 delivery fee.
- Two 24 ft garage runs: about 110 80 lb bags, or about $527.60 delivered.
- 84 ft garage perimeter: about 193 80 lb bags, or about $831.20 delivered.
- 100 ft larger wall run: about 367 80 lb bags, or about $1,469.75 delivered.
The bag counts use a common 0.60 ft3 yield for 80 lb bags. Use the yield printed on the product you plan to buy.
Common footing project scenarios
Footings are usually simple rectangular volumes, but the project type controls what must be checked before ordering concrete.
| Scenario | Calculator setup | Scope items to verify |
|---|---|---|
| Strip footing for wall | One or more continuous rectangular runs. | Width, depth, soil bearing, reinforcement, and inspection. |
| Garage perimeter footing | Total perimeter run, or grouped sides. | Slab separation, stem wall, anchor bolts, and access. |
| Interior load-bearing footing | Separate run from the exterior perimeter. | Plan dimensions, rebar, dowels, and inspection sequence. |
| Pad footing | Individual rectangular pad volume. | Use pad dimensions separately from continuous runs. |
| Deck pier or post footing | Usually round holes, not a continuous footing. | Use the round-volume workflow unless the plan calls for a rectangular pad. |
| Over-dug trench | Actual trench width and depth after excavation. | Add waste and confirm whether extra concrete is acceptable. |
This prevents a common quote problem: one bid may include excavation, reinforcement, inspection, and pump access while another only prices concrete.
Example 1: small wall footing
Assume:
- Length: 40 ft
- Width: 16 in
- Depth: 8 in
- Waste: 10%
Base volume:
40 x 16 x 8 / 144 = 35.56 ft3
35.56 / 27 = 1.32 yd3
With waste:
1.32 x 1.10 = 1.45 yd3
Planning estimate: about 1.45 cubic yards after waste.
At $165 per yd3 and a $125 delivery or short-load fee:
1.45 x $165 = $239.25
$239.25 + $125 = $364.25
This is material and delivery only. It does not include excavation, trench cleanup, rebar, forms, inspection, pump service, cleanup, or labor.
Example 2: garage footing runs
Assume two garage footing runs, each 24 ft long, 18 in wide, and 10 in deep.
Volume per run:
24 x 18 x 10 / 144 / 27 = 1.11 yd3
Two runs:
1.11 x 2 = 2.22 yd3
2.22 x 1.10 = 2.44 yd3
Planning estimate: about 2.44 yd3 after waste.
If the garage also has a slab, estimate the slab separately with the Concrete Garage Slab Calculator.
Example 3: garage perimeter footing
Assume:
- Total footing run: 84 ft
- Width: 18 in
- Depth: 10 in
- Waste: 10%
Calculation:
84 x 18 x 10 / 144 = 105 ft3
105 / 27 = 3.89 yd3
3.89 x 1.10 = 4.28 yd3
Planning estimate: about 4.28 cubic yards after waste. This is usually a ready-mix-sized order, subject to supplier minimums, access, chute reach, inspection timing, and placement method.
Example 4: larger wall footing
A 100 ft continuous footing that is 24 in wide and 12 in deep is:
100 x 24 x 12 / 144 / 27 = 7.41 yd3
7.41 x 1.10 = 8.15 yd3
That scale is typically a ready-mix planning signal. It may also require pump or buggy planning, rebar inspection, and careful placement timing.
Example 5: pad footing
Some projects use isolated rectangular pad footings instead of one continuous run. Estimate each pad as length x width x depth.
Assume four pads, each 24 in x 24 in x 12 in:
2 ft x 2 ft x 1 ft = 4 ft3 per pad
4 ft3 x 4 pads = 16 ft3
16 / 27 = 0.59 yd3
0.59 x 1.10 = 0.65 yd3 with waste
That is material quantity only. Pad footing size, reinforcement, post bases, soil, and inspection requirements should come from the plan or local code.
Deck footing and post-hole note
Deck projects often use round pier footings instead of one continuous footing. For round holes, use a cylinder formula:
cubic feet = 3.1416 x radius ft x radius ft x depth ft
For multiple identical holes:
total cubic feet = cubic feet per hole x number of holes
Round holes should usually be estimated with the Concrete Post Hole Calculator. If you need a more general round-shape workflow, the Concrete Volume Calculator still works.
Over-digging and trench shape
A footing trench rarely matches the plan perfectly. Loose soil, sloped sides, rock removal, cave-ins, water, and cleanup can increase concrete volume. If the actual trench is wider or deeper than the plan, use the actual dimensions for a material estimate.
For early planning, 5% to 10% waste is common. For rough excavation or soft soil, discuss the buffer with the contractor or supplier before ordering.
Bags or ready-mix for footings?
Small deck or shed footings may be possible with bags. Continuous wall and garage footings often become ready-mix jobs.
For the 1.45 yd3 wall footing example:
1.45 x 27 / 0.60 = 65.25 bags
round up to 66 80 lb bags
For bag yield references, see Concrete Bags per Yard. If you are deciding between bagged concrete and delivery, compare both in the Ready-Mix vs Bags Calculator.
Bag count pressure table
Footing bag counts can become large quickly because the pour is often continuous and time-sensitive.
| Bag count result | Practical meaning |
|---|---|
| Under 25 bags | Small pad or short footing territory. |
| 25 to 75 bags | Possible with bags, but mixing pace and inspection timing matter. |
| 75 to 150 bags | Compare ready-mix, short-load fees, access, and labor. |
| 150+ bags | Usually a ready-mix or contractor-pour planning signal. |
| 300+ bags | Common for large continuous footings; hand mixing is normally unrealistic. |
Continuous footings need placement consistency. A low material price from bags may not be worth it if mixing slows the pour or creates cold joints.
Supplier, DIY, or foundation contractor?
Footings sit closer to code, inspection, and structural risk than many small flatwork jobs. Use the calculator result to decide which conversation to have next.
| Result or project condition | Better next step | Why |
|---|---|---|
| Small isolated pad footing | Compare bags and local delivery. | Mobilization may dominate a tiny job. |
| 25 to 75 bags | Compare bags, rental mixer, and short-load ready-mix. | Mixing pace and inspection timing start to matter. |
| Continuous footing run | Get ready-mix pricing and access details. | Continuous placement is usually easier with delivery. |
| Permitted foundation, garage, or addition | Coordinate with contractor, inspector, or designer. | Footing size, rebar, frost depth, and inspection are not calculator decisions. |
| Poor access or deep trench | Ask about pump, buggy, wheelbarrow route, and wait time. | Placement method can change the real quote more than concrete price. |
| Trench is wider than planned | Recalculate before ordering. | Over-digging across a long run can add meaningful yardage. |
For non-structural small work, DIY bags may be reasonable. For inspected foundation work, the material estimate should support an approved plan and a scheduled pour, not replace either one.
Material cost vs project cost
For ready-mix:
ready-mix total = cubic yards after waste x price per yard + delivery fees
For bagged concrete:
bagged total = rounded bag count x price per bag
Those are material-only planning numbers. They do not include excavation, forms, rebar, chairs, dowels, anchor bolts, inspections, pump or buggy service, taxes, labor, cleanup, or contractor overhead.
Use this broader project formula when comparing quotes:
project total =
concrete material
+ delivery or short-load fees
+ excavation, trench cleanup, forms, and rebar
+ inspections, pump or buggy service, tax, cleanup, and labor
Footing buying checklist
- Confirm footing width, depth, reinforcement, and frost depth before ordering.
- Measure actual trench width and depth after excavation.
- Calculate different footing sizes separately.
- Add waste for uneven trench sides, loose soil, water, and over-digging.
- Confirm whether the pour must wait for inspection.
- Ask suppliers about minimum loads, short-load fees, waiting time, and access.
- Decide whether chute reach is enough or pump/buggy placement is needed.
- Keep material-only concrete cost separate from the full installed quote.
- Do not use a material calculator as structural design approval.
Quote checklist for footing work
Before accepting a footing bid, ask what is included in writing:
- Footing dimensions, total run length, and total cubic yards.
- Excavation, trench cleanup, forms, and spoil removal.
- Rebar size, spacing, chairs, dowels, anchors, and inspection requirements.
- Concrete mix, delivery method, pump or buggy service, and access plan.
- Pour schedule, weather plan, water handling, cleanup, and warranty.
- Permit, code, engineering, or inspection responsibilities.
That checklist helps you compare the calculator number against the scope of a real footing quote.
Inspection, rebar, and pour-timing checks
Footing concrete is often tied to inspection and reinforcement timing. Before ordering ready-mix or buying bags, confirm:
- Whether excavation must be inspected before concrete is placed.
- Rebar size, spacing, chairs, dowels, lap requirements, and anchor details.
- Whether water, loose soil, cave-ins, or soft spots must be corrected first.
- Chute reach, pump, buggy, or wheelbarrow path to the trench.
- Whether the slab, stem wall, or pier work is a separate pour.
These items usually do not change the rectangular volume formula, but they can control the schedule, delivery time, and contractor quote.
Footing bid red flags
Use these red flags before accepting a low footing quote.
| Red flag | What to ask before accepting |
|---|---|
| Only one total price | Ask for run length, width, depth, concrete yards, and pour method. |
| No rebar or inspection note | Ask whether reinforcement, chairs, dowels, anchors, and inspection timing are included. |
| Plan dimensions only after excavation | Ask whether actual trench width and depth were measured before ordering. |
| No access plan | Ask whether chute reach is enough or pump, buggy, or wheelbarrow placement is priced. |
| Slab and footing bundled together | Ask for separate footing and slab quantities so the bid can be checked. |
| No water or trench cleanup scope | Ask who handles cave-ins, loose soil, standing water, and spoil removal. |
| Very low cubic-yard allowance | Ask what happens if the trench takes more concrete than planned. |
A strong footing quote makes the dimensions, reinforcement, inspection status, access method, cleanup, and concrete quantity visible. If those items are missing, the calculator result gives you a cleaner way to ask for them.
Common footing calculation mistakes
- Using inches as feet in the formula.
- Forgetting to divide by 144 when width and depth are in inches.
- Estimating from plan dimensions after the trench is over-dug.
- Combining different footing sizes into one rough average.
- Forgetting waste for uneven trench sides and loose soil.
- Using a continuous footing calculator for round pier holes.
- Treating material-only cost as the full installed footing cost.
- Treating a calculator result as structural, code, or inspection approval.
FAQ
How much waste should I add for footings?
For early planning, 5% to 10% is common. Uneven excavation, loose soil, measurement uncertainty, water, and over-digging can require more.
Can I estimate footings with bags?
Yes for small volumes, but continuous footings often become large enough that ready-mix should be compared. Use the Concrete Bag Calculator after you know the volume.
Are footing sizes universal?
No. Footing size depends on loads, soil, frost depth, local code, and project design. Ask a qualified professional when the footing supports a structure or is regulated by code.
How many yards for a 40 ft footing?
A 40 ft footing that is 16 in wide and 8 in deep is about 1.32 yd3 before waste. With 10% waste, plan around 1.45 yd3.
How many bags for a 40 ft wall footing?
At 1.45 yd3 after waste, a common 0.60 ft3 80 lb bag yield gives about 66 bags after rounding up.
Should I calculate the slab and footing together?
Usually no. Calculate footing runs and slab areas separately, then add the material totals if they will be poured together. Separate notes make quote review easier.
Does this include labor?
No. These examples estimate concrete material only. Excavation, forms, reinforcement, inspection, pump service, cleanup, permits, tax, and labor are separate.
What if the trench is wider than the plan?
Use the actual trench dimensions for material planning. Over-digging, sloped sides, loose soil, and cave-ins can increase concrete volume. Confirm with the contractor or inspector if the extra width affects the approved design.
Do I subtract rebar volume from the concrete estimate?
Usually no. Rebar displacement is normally small compared with waste, over-digging, trench cleanup, and ordering increments. Keep reinforcement in the quote scope, but do not usually subtract it from yardage.
Can I pour footings before inspection?
Only if your local rules and project requirements allow it. Many footing jobs require excavation and rebar inspection before concrete placement. Confirm inspection timing before scheduling ready-mix.
Are deck pier holes the same as continuous footings?
No. Deck piers and post holes are often round or isolated pad footings, while continuous footings are rectangular runs. Use the round-volume calculator or estimate each pad separately when the footing is not a continuous run.
Next step
Open the Concrete Footing Calculator and enter your footing run, width, depth, waste factor, and local material price. If your project uses round holes, start with the Concrete Post Hole Calculator instead.
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.