Footing Calculator
Planning a concrete footing for a house, deck, garage, wall, shed, or other construction project requires knowing how much concrete you need. Ordering too little concrete can cause delays, while ordering too much can increase material costs and waste. Our footing calculator makes this calculation much easier by estimating the concrete volume, number of 80 lb bags required, and approximate concrete cost based on your footing dimensions.
The calculator uses the footing's length, width, and depth in feet to determine the total volume. It then converts that volume from cubic feet to cubic yards, estimates the number of 80 lb concrete bags needed, and calculates an estimated cost using the concrete price you enter.
Whether you're working on a small DIY project or preparing an initial material estimate for a larger construction job, this tool provides a quick starting point for understanding your concrete requirements.
What Is a Footing?
A footing is a structural base that helps transfer the weight of a building, wall, column, deck, or other structure into the ground. Concrete footings are commonly placed below foundations, walls, posts, and other load-bearing elements.
The dimensions of a footing can vary significantly depending on the type of structure, soil conditions, local building requirements, expected loads, and design specifications. Therefore, the dimensions you enter into a footing calculator should come from your construction plans, building requirements, or an appropriate professional recommendation.
Once you know the required dimensions, a calculator can quickly determine the approximate amount of concrete associated with those dimensions.
How Does the Footing Calculator Work?
The calculator requires four values:
- Length: The footing length in feet.
- Width: The footing width in feet.
- Depth: The footing depth in feet.
- Concrete price: The price of concrete per cubic yard.
After entering these values, select Calculate. The calculator provides four results:
- Volume in cubic feet
- Volume in cubic yards
- Estimated number of 80 lb concrete bags
- Estimated concrete cost
You can use the Reset option to start over and enter different measurements.
How to Use the Footing Calculator
Using the tool is straightforward. Follow these steps.
Step 1: Measure the footing length
Enter the total footing length in feet. For example, if your footing is 20 feet long, enter 20.
If the footing consists of several separate sections, you may need to calculate each section separately and add the results together, depending on the shape and design of the project.
Step 2: Enter the footing width
Enter the footing width in feet. For example, a footing that is 2 feet wide should be entered as 2.
Make sure the measurement represents the actual concrete footing width rather than the width of an excavation or surrounding area unless those dimensions are the same.
Step 3: Enter the footing depth
Enter the footing depth in feet. For example, if the footing is 0.5 feet deep, enter 0.5.
Accurate depth measurements are important because even a relatively small change in depth can affect the total concrete volume.
Step 4: Enter the concrete price
Enter the price of concrete per cubic yard. The calculator starts with a default price of $150 per cubic yard, but you can replace this with your local quoted price.
Concrete prices vary by location, supplier, delivery requirements, order size, concrete mix, and other factors, so using a current local quote will provide a more useful cost estimate.
Step 5: Click Calculate
After entering all four values, click Calculate. The calculator displays the estimated concrete volume, cubic yards, number of 80 lb bags, and total material cost.
Footing Calculator Formula
Understanding the basic calculation can help you verify the results.
For a simple rectangular footing, the volume in cubic feet is calculated as:
Volume = Length × Width × Depth
For example, suppose a footing is:
- 20 feet long
- 2 feet wide
- 0.5 feet deep
The volume is:
20 × 2 × 0.5 = 20 cubic feet
The calculator then converts cubic feet to cubic yards because ready-mix concrete is commonly priced and ordered by the cubic yard.
There are 27 cubic feet in one cubic yard, so:
Cubic yards = Cubic feet ÷ 27
For the example:
20 ÷ 27 = 0.74 cubic yards
The calculator displays the result rounded to two decimal places.
Footing Calculator Example
Let's consider a practical example.
Suppose you're calculating a rectangular concrete footing that measures:
- Length: 30 feet
- Width: 2 feet
- Depth: 0.5 feet
- Concrete price: $150 per cubic yard
First, calculate the volume:
30 × 2 × 0.5 = 30 cubic feet
Next, convert cubic feet to cubic yards:
30 ÷ 27 = 1.11 cubic yards
The calculator therefore reports approximately 1.11 cubic yards of concrete.
The estimated number of 80 lb bags is calculated from the cubic-foot volume. The calculator assumes each 80 lb bag represents approximately 0.6 cubic feet of concrete.
Therefore:
30 ÷ 0.6 = 50 bags
Finally, the estimated concrete cost is calculated using the cubic-yard quantity:
1.11 × $150 = approximately $166.67
This example demonstrates how changing any of the dimensions can significantly change the amount of concrete required.
How Many 80 lb Bags of Concrete Do You Need?
One of the useful features of this footing calculator is its estimate of 80 lb concrete bags.
The calculator uses an assumed yield of approximately 0.6 cubic feet per 80 lb bag. The calculation is:
Number of bags = Cubic feet ÷ 0.6
The result is rounded up to the next whole bag because you cannot purchase a fraction of a bag.
For example, if a project requires 10 cubic feet:
10 ÷ 0.6 = 16.67
The calculator rounds this up to 17 bags.
Keep in mind that actual bag yield can vary by product. Always check the manufacturer's coverage or yield information printed on the specific concrete mix you intend to purchase.
How Is Concrete Cost Calculated?
The calculator estimates concrete cost based on the cubic-yard volume and the price entered per cubic yard.
The formula is:
Estimated Cost = Cubic Yards × Price Per Cubic Yard
For example, if your project requires 2 cubic yards and your quoted price is $150 per cubic yard:
2 × $150 = $300
This is an estimate of the concrete material cost based on the entered price. It should not automatically be treated as the final project cost.
Additional expenses may include delivery, labor, pumping, reinforcement, forms, excavation, site preparation, taxes, minimum-order charges, or other supplier fees.
Ready-Mix Concrete vs. Bagged Concrete
The calculator provides both cubic-yard and 80 lb bag estimates, which can be useful when deciding how to source concrete.
Ready-mix concrete is commonly delivered by truck and is generally measured in cubic yards. It can be practical for projects requiring a larger volume of concrete.
Bagged concrete is purchased in individual bags and mixed on site. It may be convenient for smaller projects where ordering a concrete truck is unnecessary.
The appropriate option depends on the project's size, access to the site, labor available, local pricing, and the requirements of the construction work.
Why Accurate Footing Measurements Matter
Small measurement errors can affect the final concrete estimate. Because volume depends on multiplying length, width, and depth, an error in any of these measurements changes the calculated quantity.
Before using the calculator, verify that:
- Measurements are in feet.
- Length, width, and depth are measured consistently.
- The dimensions correspond to the actual footing design.
- The concrete price is entered per cubic yard.
- You have checked the expected yield of your selected bagged concrete product.
For irregularly shaped footings, you may need to divide the project into multiple simple sections and calculate each section independently.
Should You Order Exactly the Calculated Amount?
A calculator provides an estimate, but ordering exactly the calculated quantity may not always be appropriate for a real construction project. Actual site conditions can affect the amount of concrete needed.
Excavation variations, uneven ground, spillage, form dimensions, and other factors can increase material requirements.
For ready-mix concrete, discuss the required quantity with your concrete supplier or contractor before placing an order. For structural footings, follow the construction plans and applicable local requirements rather than relying solely on a material calculator.
Common Footing Calculation Mistakes
Several simple mistakes can produce an incorrect estimate.
Mixing measurement units
The calculator expects measurements in feet. If your measurements are in inches, convert them to feet first.
For example:
6 inches = 0.5 feet
Entering 6 instead of 0.5 would dramatically change the result.
Forgetting the depth
Concrete volume requires three dimensions. Using only length and width is not enough for a rectangular footing calculation.
Using the wrong concrete price
The calculator expects the price per cubic yard. A price for an individual bag should not be entered into the concrete-price field.
Ignoring product yield
Different bagged concrete products may have different yields. The calculator uses an assumed 0.6 cubic feet per 80 lb bag, so verify the actual product specifications before purchasing.
Calculating an irregular footing as one rectangle
If the footing has multiple sections or an unusual shape, a single length × width × depth calculation may not represent the entire project accurately.
Tips for Getting a More Accurate Estimate
For the best results, use precise measurements and current pricing.
Measure the footing dimensions carefully and convert all measurements to feet before entering them. If the footing contains multiple sections, calculate the volume of each section and combine the results.
For cost estimates, contact local concrete suppliers for current pricing. Ask whether the quoted price includes delivery and whether there are minimum order quantities or additional fees.
For structural projects, also confirm that the footing dimensions themselves are appropriate. A calculator can determine the quantity of concrete for dimensions you provide, but it does not determine whether those dimensions are structurally suitable for your project.
Who Can Use a Footing Calculator?
A footing calculator can be useful for homeowners, DIY builders, contractors, landscapers, construction students, and anyone preparing a preliminary concrete material estimate.
It can help with projects involving foundation footings, deck footings, retaining-wall-related work, small outbuildings, posts, walls, and other rectangular concrete applications.
However, the tool is primarily a material estimation tool. Structural design decisions should be based on appropriate plans, engineering requirements, soil conditions, and local building regulations.
Frequently Asked Questions
1. What is a footing calculator?
A footing calculator estimates the concrete volume required for a rectangular footing based on its length, width, and depth. It can also estimate cubic yards, 80 lb concrete bags, and material cost.
2. What measurements do I need?
You need the footing's length, width, and depth. All three measurements should be entered in feet.
3. How do I calculate footing volume?
For a rectangular footing, multiply length by width by depth. The result is the volume in cubic feet.
Length × Width × Depth = Cubic Feet
4. How many cubic feet are in a cubic yard?
One cubic yard contains 27 cubic feet. To convert cubic feet to cubic yards, divide the cubic-foot volume by 27.
5. How many 80 lb bags does the calculator estimate?
The calculator estimates bags using an assumed yield of 0.6 cubic feet per 80 lb bag and rounds the result up to the next whole bag.
6. Can I use the calculator for bagged concrete?
Yes. The calculator provides an estimated number of 80 lb bags based on the assumed 0.6 cubic-foot yield.
7. Can I use the calculator for ready-mix concrete?
Yes. The cubic-yard result can help provide a preliminary estimate for ready-mix concrete. Confirm the final order quantity with your concrete supplier.
8. What price should I enter?
Enter your concrete price per cubic yard. If your supplier quotes a different unit, convert the price to a per-cubic-yard figure before entering it.
9. Why does the calculator show both cubic feet and cubic yards?
Cubic feet makes it easy to understand the basic volume calculation, while cubic yards are commonly useful for estimating ready-mix concrete quantities and costs.
10. Can I calculate the cost of a footing?
Yes. Enter the concrete price per cubic yard, and the calculator multiplies that price by the estimated cubic-yard volume.
11. Does the calculator include labor?
No. The estimated cost is based on the calculated concrete volume and entered concrete price. Labor and other construction expenses are not included.
12. Does the estimate include concrete delivery?
No. Delivery charges are not automatically included. Ask your local supplier whether delivery, pumping, taxes, or other fees apply.
13. Can I calculate a circular footing?
This calculator is designed around length × width × depth, so it is intended for rectangular volumes. A circular footing requires a different volume formula.
14. Can I use inches instead of feet?
The calculator's inputs are designed for feet. Convert inch measurements to feet before entering them. For example, 12 inches equals 1 foot.
15. Is the footing calculator suitable for structural design?
The tool can estimate concrete quantities, but it does not determine the correct structural dimensions of a footing. Follow approved construction plans and applicable local requirements for structural projects.
Final Thoughts
A footing calculator is a convenient way to estimate how much concrete a rectangular footing requires. By entering the length, width, depth, and concrete price, you can quickly see the estimated volume in cubic feet and cubic yards, the approximate number of 80 lb concrete bags, and the estimated material cost.
Use the calculator early in your planning process to understand material requirements and compare potential costs. For the most reliable purchasing estimate, verify your measurements, check the yield of your selected concrete product, and obtain current pricing from a local supplier.
Most importantly, remember that concrete quantity calculations and structural footing design are two different things. The calculator can help answer “How much concrete will these dimensions require?”, while an appropriate construction professional, engineer, building plan, or local authority may be needed to determine “What should the footing dimensions be?”