AtlasCalcsUtility Calculation Suite
2026-09-23 8 min read

Combined Footing Calculator

Free combined footing calculator — calculate combined footing concrete with rebar grids, count and cost. Includes live results, step-by-step working, charts, material takeoff and cost estimates. No sign-up.

Calculator

Pad count(pads)
pads
Pad length(ft)
ft
Pad width(ft)
ft
Pad depth(in)
in
Bar spacing(in) Help
in

Grid each way

Waste allowance(%) Help
%

Over-excavation and spillage

Price (optional)($/cu yd) Help
$/cu yd

Blank to skip

Bar size

Footing plan

ItemAmount
ConcreteAll pads + waste3.804 cu yd
Each padSingle pad1.778 cu yd
Rebar grid152 ft102 lb

How to use this result

  • Primary result: 3.80 cu yd — verify it against a rough hand check before ordering.
  • Read the steps section to see every conversion and the exact formula path.
  • Use the breakdown table on the left as your order or bid checklist.
  • Re-run with worst-case dimensions so the plan covers the whole job.

Results

Optimal

Concrete to order

3.804cu yd

All pads + waste

Each pad

1.778cu yd

Single pad volume

Rebar grid

102lb

152 ft total

Live results update as you type — currently showing 3.80 cu yd. Replace the defaults with your own measurements for exact results.

Visualizations

Order vs one pad (cu yd)

3.8Order
1.8One pad

Net vs waste

Net93%
Waste7%

Formula

Pad footing concrete is single-pad volume times count, with a rebar grid each way.

V = n × L × W × D ÷ 27

Variables

SymbolNameUnitDescription
nCountpadsNumber of pads.
L, W, DPad sizeftDepth converts from inches.
gridSteelftBars each way at spacing.

Explanation

Single pad at full precision times count; grid bars count from spacing; waste gives the order.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

One pad in cubic yards.

8 × 4 × 1.50 ÷ 27
Result: Each = 1.778 cu yd
Step 2

Grid steel at 12 in centers each way.

(5 × 8.00) + (9 × 4.00) × 2
Result: 152 ft rebar
Step 3

Total with 7% waste.

3.556 × 1.07
Result: Order = 3.804 cu yd
Final Answer
3.804

Worked Examples

See how the calculator works with different scenarios.

Scenario

The calculation run on the values above, showing the full path rather than only the answer.

Inputs

Result:3.80 cu yd

Calculation

1. One pad in cubic yards. → Each = 1.778 cu yd 2. Grid steel at 12 in centers each way. → 152 ft rebar 3. Total with 7% waste. → Order = 3.804 cu yd

Result

3.80 cu yd

Interpretation

Confirm bearing soil and frost depth, hold inspections before pouring, and keep 5–10% concrete waste in every order.

Understanding Your Result

Your Result: Concrete to order: 3.804 cu yd

Typical range: Strip footing ~1–2 cu yd per 10 ft · pier 12 in × 4 ft ~0.13 cu yd · basement wall 40 ft ~10 cu yd.

What This Means

Your result is 3.80 cu yd — the concrete, excavation, rebar and cost for your combined footing

Why It Matters

Foundations carry everything and forgive nothing: undersized footings settle, missing rebar cracks, and wet concrete waits for no one. Quantities first keeps the pour boring.

Professional Interpretation

Confirm bearing soil and frost depth, hold inspections before pouring, and keep 5–10% concrete waste in every order.

How this is calculated

Volume is count × length × width × depth-in-feet ÷ 27. Waste and rounding apply last.

What drives the result

The inputs in a single consistent unit and the allowance or price you apply.

Recommendations

  • •Verify critical dimensions on site before ordering.
  • •Keep one unit throughout each calculation.
  • •Add the trade allowance before buying, not after.
  • •Attach the step-by-step working to bids and records.

Educational Content

Introduction

Foundation quantity is geometry: lengths × cross-sections for concrete, perimeter × depth for excavation, bar counts × lengths for rebar.

Concept Explanation

Volume is count × length × width × depth-in-feet ÷ 27. Waste and rounding apply last.

Applications

▸Strip, pad and pier footing takeoffs
▸Foundation wall and slab concrete
▸Excavation, backfill and gravel quantities
▸Rebar, formwork and drainage counts
▸Foundation cost estimates with waste

Benefits

  • •Concrete, dig, steel and cost from one input set
  • •Inspection-ready step-by-step working
  • •Waste and rounding built into order rows
  • •Free, no sign-up, works on site from a phone

Limitations

  • •Two-dimensional math unless stated otherwise — slopes and curves need the right tool
  • •Results are only as good as the site measurements
  • •Allowances and prices are estimates — confirm with local quotes

Best Practices

  • •Measure twice and write measurements down before typing them in
  • •Keep one unit throughout each calculation
  • •Photograph the tape on large or disputed measurements
  • •Re-run with worst-case numbers so the plan covers the whole job

Common Misconceptions

Myth: The calculator replaces site verification.
Truth: It replaces the arithmetic, not the tape measure — always verify before ordering.
Myth: One decimal place is always enough.
Truth: On long runs, rounding early compounds. Enter full measurements and let the tool round at the end.
Myth: Metric and imperial give different answers.
Truth: They are the same physical quantity in different units — conversion is exact.

Practical Tips

  • •Enter full measurements and let the tool round at the end.
  • •Use the steps section to double-check the formula path.
  • •Save or share the result link with the crew and the supplier.
  • •Re-run with worst-case dimensions for a safe order.

Common Mistakes

Rounding measurements before calculating.
Enter the full tape reading; rounding early compounds across a job.
Mixing units between fields.
Pick one unit in the dropdown so every conversion is consistent.
Forgetting to verify on site.
Plans differ from as-built work — confirm critical dimensions.
Ordering the bare result with no allowance.
Add the trade waste or contingency factor before buying.

Assumptions

This calculator makes the following assumptions to provide estimates:

Consistent units: All inputs share the selected unit system.
Standard geometry: Flat-plane Euclidean formulas unless stated.
Full precision: Rounding happens only on display, never mid-calculation.

Limitations

Be aware of these limitations when using this calculator:

Estimates, not quotes: Allowances and unit prices vary by region — get 2–3 local quotes.
Verify on site: Confirm critical dimensions before ordering or cutting.

Frequently Asked Questions

Answers to common questions about this calculator.

How do I calculate concrete for a combined footing?
One pad is length × width × depth ÷ 27; multiply by the pad count and add 5–10% waste. Grids at 12 in centers each way are standard.
When are pad footings used?
Under individual columns, posts and piers where loads are points rather than wall lines. Size follows soil capacity — the drawings govern.
How accurate is this calculator?
Exact for the dimensions entered. Soil capacity, frost depth and water table govern the design — verify with the drawings and the inspector.
What does the cost estimate include?
Concrete and listed materials at your prices on the order quantities. Excavation, labor, pumping and inspections add per the cost rows.
Do I need an engineer?
Standard house footings follow prescriptive IRC tables; anything unusual — poor soils, slopes, deep fills, tall walls — needs engineering.
When can footings be poured?
After the excavation passes inspection: correct depth, clean undisturbed bearing, setbacks held and forms/rebar approved.
How wide and deep should a footing be?
Width follows bearing capacity and wall load, depth follows frost line and drawings — this tool quantities the chosen size. Never guess structural sizes.
How do footings reach below frost?
Excavate to local frost depth (12 in in warm zones, 48 in+ in cold ones) and bear on undisturbed soil. The inspector checks depth before concrete.
How much rebar goes in a footing?
Typically two or more continuous bars with corner laps; pads get grids each way. Bar count, size and laps total the footage in this tool.
How do I lap and corner rebar?
Overlap 24–30 in for #4 (more for bigger bars), wire every splice, stagger laps so joints do not align, and bend corners continuous instead of butting.
What concrete strength for footings?
Usually 2,500–3,000 psi minimum per code and drawings, air-entrained where freeze-thaw reaches. Strength is specified on the plans.
How much digging is a footing really?
Roughly 1.5–2 times neat volume with working room each side and depth. Spoil swells ~25% loose — plan the pile before the excavator arrives.
What is undisturbed bearing soil?
Soil never excavated, filled or softened — footings bear only on it (or engineered fill). Mushy bottoms get over-excavated and replaced, then inspected.
Do footings need formwork both sides?
Neat cuts in firm soil can pour against earth; anything over-dug or shallow needs both faces formed. Forms also hold line and level.
How do piers differ from pad footings?
Piers are deep round shafts for point loads and frost bypass; pads are shallow square spreads. Both math out as volume, but construction differs completely.
What is a grade beam vs a strip footing?
Strip footings spread wall loads to soil; grade beams span between piles or pads carrying walls across weak ground. Different structures, similar concrete math.
How do I keep a footing pour continuous?
Stage trucks 15–20 minutes apart, vibrate into the previous face, and never let concrete sit past initial set. Small footings should pour in one go.
Why is my result different from my supplier quote?
Quotes include delivery, minimums, pack-size rounding, tax and regional pricing on top of bare quantities. Compare the net quantities first, then the add-ons.
Do I need a professional for this work?
Measuring and budgeting you can do yourself with this tool. Structural design, permits, licensed trades and inspections still need qualified professionals.
How do I convert the result to other units?
Use the results dashboard conversions, or the dedicated conversion calculators for length, area, volume and weight. Convert each linear dimension before combining into areas or volumes.
What mistakes do beginners make with the combined footing calculator?
Rounding measurements too early, mixing units between fields, ordering the bare result with no allowance, and skipping site verification. The mistakes section on the page covers each one.
Can I share the combined footing calculator result with my crew or supplier?
Yes — use the Share result button to send the headline figure and link. The supplier can re-run your numbers from the same inputs.
Does the combined footing calculator work on a phone at the job site?
Yes — every page is mobile-friendly with no sign-up. Bookmark the tools you use daily for one-tap takeoffs.
How often should I re-run the combined footing calculator?
Re-run whenever dimensions change, prices move, or you switch materials. Early estimates, pre-order checks and final buy quantities each deserve a fresh run.
What should I check before ordering materials?
Dimensions verified on site, correct unit, waste allowance added, pack sizes and minimums confirmed, delivery access and schedule agreed. The breakdown table is your checklist.
Where do I find the formula behind the combined footing calculator?
In the formula section below the results, with every variable defined, plus a worked example tracing your own inputs step by step.
How do I read the steps section on the combined footing calculator page?
Each numbered step shows the inputs used, the formula applied and the intermediate result, ending in the headline figure. Follow it top to bottom to audit the math.
What if my site conditions differ from the page defaults?
Defaults are worked examples, not recommendations — replace every input with your own measurements, prices and allowances before ordering or bidding.
How do I budget for price changes mid-project?
Lock supplier quotes in writing with expiry dates, carry a 5–10% escalation contingency, and re-run the calculator when prices move. Volatile materials get shorter quote windows.
Should I buy materials in bulk for this job?
Bulk wins when storage is dry and secure, the material keeps, and the discount beats carrying cost. Otherwise phased delivery avoids damage, theft and cash lockup.

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Glossary

Technical terms used in mortgage calculations explained in plain language.

Footing
Widened base that spreads wall or column loads to the soil.
Bearing capacity
Soil pressure limit, e.g. 1,500–4,000 psf for typical soils.
Rebar
Deformed steel bars; #4 is 1/2 in, #5 is 5/8 in diameter.
Frost line
Depth below which soil does not freeze — footings must bear below it.
Backfill
Soil replaced around the foundation after inspection.
Waterproofing
Membrane or coating keeping foundation walls dry.
cu yd
The primary unit reported by this calculator.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

IRC Chapter 4: footing sizes, depths and reinforcement minimumsFootings bear on undisturbed soil below the local frost lineConcrete 5–10% waste; rebar laps per ACI 318 development lengthsInspect footings before pouring — no inspection, no concrete

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Page Information

Last Updated:

2026-09-23

Version:

2.0.0

License:

Free to use for educational and professional purposes.