Concrete Footing Calculator
Calculate concrete volume, cubic yards to order, bag count, waste allowance, estimated cost, and concrete weight for strip, pad, and round footings.
Calculator is for informational purposes only. Terms and Conditions
Choose footing type
Select the footing geometry and unit preset before entering dimensions.
Enter the known values
Inputs update based on the selected footing type.
Visual Check
Use the diagram to verify the selected footing shape and dimensions.
Solution
Live result, concrete bags, cost estimate, warnings, and solution steps.
Quick checks
- Check—
Show solution steps See geometry, unit conversions, substitutions, assumptions, and final estimate
- Enter values to see the full calculation steps and checks.
Source, Standards, and Assumptions
Calculation basis, constants, assumptions, and limitations.
The calculator uses standard geometric volume formulas and common concrete estimating unit conversions.
- Assumptions will appear after a valid calculation.
On this page
Calculator Guide
How to Use the Concrete Footing Calculator
The Concrete Footing Calculator above estimates how much concrete you need for strip footings, pad footings, and round pier or sonotube footings. Enter the footing dimensions, quantity, waste factor, and bag or ready-mix cost settings to calculate cubic yards, cubic feet, bag count, estimated cost, and concrete weight.
Use the result as a material estimate, not as structural approval. A concrete footing may also need to satisfy local frost depth, soil bearing, reinforcement, permit, and building-code requirements.
Quick Answer
To calculate concrete for a rectangular footing, multiply length by width by depth, then multiply by the number of footings. If the dimensions are in feet, divide cubic feet by 27 to get cubic yards. For round footings, use \( \pi r^2D \), then multiply by quantity and add waste.
When not to rely on the calculator alone
Do not use this concrete footing calculator as the only basis for structural design. The calculator estimates quantity and cost; it does not check frost depth, soil bearing pressure, settlement, uplift, sliding, overturning, rebar, or local code compliance.
Inputs and Outputs Used by the Calculator
The calculator uses footing shape, dimensions, quantity, waste, and cost assumptions to estimate the concrete needed. The most important step is selecting the correct footing type before entering dimensions.
Choose strip footing when
You are estimating a long continuous footing below a foundation wall, masonry wall, retaining wall, or other linear support.
Choose pad footing when
You are estimating a square or rectangular isolated footing below a column, post base, shed support, or similar load point.
Choose round pier when
You are estimating a cylindrical post hole, deck pier, pole support, fence post footing, or sonotube footing.
| Type | Value | What It Means | Common Unit |
|---|---|---|---|
| Input | Footing type | Choose strip, pad, or round pier/sonotube so the calculator uses the correct geometry. | selection |
| Input | Length, width, and depth | Used for rectangular, pad, and strip footings. Measure the concrete footing, not just the wall or post. | ft, in, m, cm |
| Input | Diameter and depth | Used for round piers, post holes, and sonotubes. Diameter is converted to radius in the formula. | in, ft, cm, m |
| Input | Quantity | The number of repeated footings, pads, or piers included in the estimate. | count |
| Input | Waste factor | Extra concrete added for over-excavation, uneven holes, spillage, and ordering safety. | % |
| Output | Concrete to order | The waste-adjusted volume of concrete needed for the footing project. | yd³, ft³, m³ |
| Output | Bag count and cost | Estimated number of 40 lb, 60 lb, or 80 lb bags and the approximate bagged concrete cost. | bags, USD |
Concrete Footing Formula
The formula depends on the footing shape. Rectangular footings use length, width, and depth. Round footings use radius and depth. In both cases, the calculator multiplies by quantity and adds the selected waste factor.
Rectangular, Strip, or Pad Footing
Use this for continuous wall footings, rectangular pads, square pads, and other box-shaped footing volumes.
Round Pier or Sonotube Footing
Use this when the footing is a round hole, cylindrical pier, post footing, or sonotube.
Cubic Yards Conversion
Concrete is commonly ordered in cubic yards, so a cubic-foot result is divided by 27.
Concrete Bag Count from Cubic Yards
Use this shortcut when you already know the cubic yards and want to estimate how many bags to buy.
What the Variables Mean
Each variable represents either a measured footing dimension, a quantity multiplier, or an estimating adjustment. Converting dimensions to the same unit before multiplying is essential.
\(V_{order}\)
The waste-adjusted concrete volume to order. The calculator can show this in cubic yards, cubic feet, or cubic meters.
\(L\), \(W\), and \(D\)
Length, width, and depth of a rectangular footing. Use feet for hand calculations that will be converted to cubic yards.
\(d\) and \(r\)
\(d\) is the diameter of a round footing, and \(r=d/2\) is the radius. Round footing volume depends on radius squared.
\(n\)
The number of identical footings. For one continuous strip footing, use \(n=1\). For repeated piers, use the total count.
\(w\)
The waste or overage percentage. This accounts for rough excavation, uneven forms, spillage, and ordering safety.
Bag yield
The approximate volume produced by one bag of concrete mix. Common estimating yields are 0.30 ft³, 0.45 ft³, and 0.60 ft³.
How to Use the Calculator
Use the calculator by matching the footing shape to your project, entering the actual concrete dimensions, and checking the output against the formulas above. The calculator does the unit conversion, waste adjustment, bag rounding, and cost estimate for you.
Select the footing type
Choose strip or wall footing for long continuous footings, pad footing for rectangular supports, or round pier/sonotube footing for cylindrical holes.
Enter the footing dimensions
Enter the concrete length, width, depth, or diameter. For a wall footing, use the total footing length. For repeated posts, enter the dimensions for one post footing and the total quantity.
Add waste and cost settings
Use 5% to 10% waste for clean formed work and 10% to 15% or more for rough hand-dug holes. Add bag cost, ready-mix cost, and delivery fee if you want a cost comparison.
Review yards, bags, and warnings
Use the cubic-yard result for ready-mix ordering and the bag count for small projects. Check the warnings if the footing is shallow, narrow, unusually large, or likely controlled by code.
How to Interpret the Result
The calculator result tells you the amount of concrete to plan for, not whether the footing is structurally adequate. A realistic result should match the size of the footing, the number of footings, and the selected waste factor.
What to do with the result
Use cubic yards for ready-mix planning, bag count for small pours, and concrete weight for hauling or jobsite handling checks.
What changes the result most?
Depth directly multiplies volume. For round piers, diameter is even more sensitive because radius is squared in \( \pi r^2D \).
Sanity check
One cubic yard equals 27 cubic feet. If the calculator returns many yards for a small post hole, the diameter, depth, or unit selection is probably wrong.
What is a suspicious result?
A result can be suspicious if a small deck pier requires hundreds of bags, a foundation wall footing returns less than a few bags, or switching units changes the result by an order of magnitude. Recheck inches versus feet first.
Input Checklist Before You Trust the Answer
Most concrete footing estimate errors come from measuring the wrong dimension, mixing inches and feet, or forgetting that round footing volume is based on radius, not diameter.
Measure the footing, not the structure
Use the full footing width and depth, not the wall thickness, post size, or column size.
Check inches versus feet
A 12-inch depth is 1 foot. Accidentally entering 12 feet instead of 12 inches creates a result 12 times too high.
Use inside diameter for tubes
For sonotubes or round forms, use the inside concrete diameter so the volume matches the concrete-filled space.
Use a whole-number quantity
Footing quantity should normally be a whole number. If you have different footing sizes, calculate each group separately.
Worked Example
These examples follow the same logic as the calculator. The first example shows a rectangular strip footing, while the second example shows a round pier or sonotube footing.
Formula
Substitution
Convert to cubic yards
Estimate 80 lb bags
Final answer
Order about 1.47 cubic yards of concrete, or about 66 bags of 80 lb concrete mix. This is reasonable because the base footing volume is 36 ft³ before the 10% waste allowance.
Formula
Base volume
Add waste
Convert to cubic yards
Estimate 80 lb bags
Final answer
For six 12-inch diameter piers that are 48 inches deep, order about 0.77 cubic yards of concrete, or about 35 bags of 80 lb mix. This result is reasonable because each pier is a small cylinder, but the quantity and depth add up quickly.
How to Visualize the Calculation
Concrete footing volume is the amount of three-dimensional space inside the footing form or excavated hole. A rectangular footing is a box-shaped volume, while a round pier is a cylindrical volume.
Rectangular footings use length × width × depth, while round piers use π × radius² × depth. Add quantity and waste factor after calculating the basic shape volume.
Reference Checks for Concrete Footing Estimates
Reference values help you spot obvious mistakes before ordering concrete. These are estimating checks, not structural design rules.
| Reference | Typical Value | How to Use It |
|---|---|---|
| Cubic yard conversion | 1 yd³ = 27 ft³ | Divide cubic feet by 27 when ordering ready-mix concrete. |
| 40 lb bag yield | About 0.30 ft³ | One cubic yard takes about 90 bags of 40 lb concrete mix. |
| 60 lb bag yield | About 0.45 ft³ | One cubic yard takes about 60 bags of 60 lb concrete mix. |
| 80 lb bag yield | About 0.60 ft³ | One cubic yard takes about 45 bags of 80 lb concrete mix. |
| Concrete weight estimate | About 150 lb/ft³ | Useful for hauling, handling, and approximate load planning. |
Bag count check
Because one cubic yard is 27 ft³, and one 80 lb bag commonly yields about 0.60 ft³, one cubic yard takes about \(27/0.60=45\) bags of 80 lb concrete mix.
Design Notes and Practical Ranges
Footing volume is only one part of footing planning. The calculator helps estimate concrete, but the actual footing size may be controlled by structure type, load, soil, frost depth, uplift, lateral loads, and local code.
Waste factor
Use about 5% for clean formed footings, 10% for typical work, and 10% to 15% or more for rough holes or over-excavation.
Bags versus ready-mix
Bagged concrete is practical for small quantities. Once the estimate reaches dozens of bags, ready-mix may be faster and easier.
Footing depth
Depth may need to account for frost protection, soil conditions, and code. Do not assume a quantity estimate verifies depth.
Rebar and reinforcement
Many structural footings use reinforcement, but requirements depend on the structure, loads, soil, and local code or engineered plans.
Units and Conversions
Concrete footing estimates are especially sensitive to unit mistakes because volume multiplies three dimensions together. Always convert inches to feet before doing a manual cubic-yard calculation.
Important Unit Conversions
For metric work, use cubic meters directly or allow the calculator to convert from millimeters, centimeters, or meters.
Hidden unit trap
Entering 12 as feet instead of 12 inches makes the depth twelve times larger. In a volume calculation, that mistake can turn a small footing estimate into a major over-order.
Bags vs Ready-Mix Concrete
Bagged concrete and ready-mix concrete can both work for footings, but they fit different project sizes. The calculator gives both estimates so you can compare material cost, labor, delivery, and placement speed.
Bagged concrete is usually better when
- The footing volume is small.
- You only need a few post holes or small pads.
- Truck access is difficult or delivery fees are too high.
- You can mix and place the concrete before it starts setting.
Ready-mix is often better when
- The project approaches one cubic yard or more.
- The bag count becomes too high to mix efficiently.
- The footing needs faster, continuous placement.
- Labor savings outweigh delivery or short-load fees.
Common Mistakes
The most common concrete footing calculator mistakes are simple: wrong units, wrong shape, missing quantity, or forgetting waste. These mistakes can cause major ordering problems.
Do
- Use the total strip footing length, not one wall segment unless calculating one segment only.
- Use the full concrete depth, not just the depth below grade.
- Round bag counts up to the next whole bag.
- Use a larger waste factor for rough hand-dug holes.
Don’t
- Do not enter diameter where the formula expects radius in a manual calculation.
- Do not assume a concrete quantity estimate approves footing size.
- Do not ignore short-load fees when comparing ready-mix to bags.
- Do not forget to calculate different footing sizes separately.
Troubleshooting Unrealistic Results
If the result looks too high, too low, or physically unrealistic, check units and geometry first. Most suspicious results come from entering inches as feet, using the wrong footing type, or miscounting repeated footings.
Result is too high
Check whether width, depth, or diameter was entered in feet instead of inches. For round piers, check diameter carefully because radius is squared.
Result is too low
Confirm you included the number of footings, used the full depth, and added a realistic waste factor.
Bag count is huge
Compare the total cubic yards to ready-mix. More than a few dozen bags can become a labor and timing problem.
Ready-mix cost seems wrong
Check cost per cubic yard, delivery fee, and whether the supplier has a minimum order or short-load fee.
Assumptions and Limitations
This calculator is designed for concrete quantity estimating. It uses standard geometric volume formulas, common bag yield assumptions, and user-entered waste and cost values.
Quantity estimate only
The calculator estimates concrete volume, bag count, cost, and weight. It does not design the footing.
Shape simplification
The formulas assume rectangular or cylindrical geometry. Irregular excavations may require a higher waste factor or separate calculations.
Bag yield variation
Actual yield can vary by product, mixing water, consolidation, and field conditions. Check the bag label for final ordering.
Code and engineering review
Final footing dimensions may require local code review, soil evaluation, reinforcement design, permits, or a qualified professional.
Key Terms
These terms help connect the calculator inputs, formula, and concrete ordering result.
Footing
A concrete support element that spreads load into the soil below a wall, post, pier, column, or foundation.
Cubic yard
A concrete volume equal to 27 cubic feet. Ready-mix concrete is commonly ordered in cubic yards.
Waste factor
Extra concrete added to the calculated volume to account for spillage, uneven excavation, over-digging, and ordering safety.
Sonotube
A round form used to create cylindrical concrete piers or post footings.
Bag yield
The approximate concrete volume produced by one bag of mix after water is added and the concrete is placed.
Frost depth
The depth to which ground may freeze in a local area. Structural footing depth may be controlled by frost protection requirements.
Concrete Footing Calculator FAQ
How do I calculate concrete for a footing?
For a rectangular footing, multiply length by width by depth, then multiply by quantity. If the dimensions are in feet, divide cubic feet by 27 to get cubic yards. For a round footing, use \( \pi r^2D \), then multiply by quantity.
How many 80 lb bags of concrete are in one cubic yard?
One 80 lb bag commonly yields about 0.60 ft³. Since one cubic yard is 27 ft³, one cubic yard requires about \(27/0.60=45\) bags of 80 lb concrete mix.
How much extra concrete should I order for footings?
Most footing projects should include 5% to 10% extra concrete. Use 10% to 15% or more for rough holes, uneven excavation, over-digging, or uncertain measurements.
Is bagged concrete or ready-mix better for footings?
Bagged concrete is usually practical for small footings. Ready-mix is often more practical when the project approaches a cubic yard, requires dozens of bags, or needs faster continuous placement.
Does this calculator determine footing size for code compliance?
No. The calculator estimates concrete quantity, bag counts, and cost. It does not verify footing width, frost depth, soil bearing, rebar, permits, or structural code compliance.