Concrete Calculator – Find Yards or Bags for a Slab or Footing
Calculate the yards of concrete needed to pour a slab, patio, footing, column, or post fill-project, and estimate the cost of materials. Plus, calculate the number of pre-mix bags needed.
Calculate Concrete for a Rectangular Slab
Calculate Concrete for a Circular Slab
Calculate Concrete for a Footing
Calculate Concrete for a Circular Column
Calculate Concrete for a Solid Wall
How to Estimate Concrete in Yards
Concrete is sold by the cubic yard, or in pre-mixed bags. A cubic yard is just a standard volume, measured in yards.
It’s important to calculate the amount of material needed as accurately as possible since you often only get one chance for the pour.
We’ll cover the process for estimating concrete in detail below, but you can also use the calculator above to simplify the process.
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Steps to Estimate
Measure the length, width, and height of the slab, footing, or column. If the area is complex or if multiple pours are needed, break the project into smaller pieces and calculate the concrete needed for each individually. For instance, if you are measuring a slab that is not a rectangle or circle, break it into different sections and measure the yards needed for each section first, then add them together.
- Convert dimensions to feet if they aren’t in feet. Convert inches to feet, convert yards to feet or convert meters to feet
- Multiply the width times the length times the height (W x L x H). You can also use our volume calculator to find cubic yardage of a space.
- Convert the volume to cubic yards from cubic feet. To do so, divide the cubic footage by 27 to get the yards of concrete needed.
- Round up to the nearest yard as most suppliers will likely not sell fractions of a yard. It is worthwhile to ask your supplier if they will sell a partial yard of material, but the most do not.
Estimate how many pre-mixed bags needed for smaller projects. For smaller projects, it may not be practical to order a truckload of concrete and pre-mixed bags make the most sense. You can purchase pre-mix bags from your local home center.
Refer to table below that shows the coverage of different sizes of pre-mix bags. On average it will take 90x 40 lb bags, 60x 60 lb bags, or 45x 80 lb bags to fill one cubic yard of concrete.
- Add 5%-10% additional material to account for settling, spillage, and waste. This will ensure you can complete your project in a single pour without needing to get more concrete to complete the project if you’re short.
Formulas for Calculating Concrete in Yards
Square and Rectangular Areas
Circular and Cylindrical Areas
yds3 = (π × radius ft × radius ft × height ft) / 27
Divide the steps into rectangles, then find the volume for each rectangle/cube. Add the volume for each rectangle to find the total volume.
volume = width × length × height
yds3 = (width ft × length ft × height ft) / 27
Use our concrete steps calculator to easily estimate material for steps.
For more complex shapes see our volume calculator.
How Many Pre-mix Bags of Concrete do you Need?
If your project is small, you can use pre-mixed bags of concrete. Bags come in 40-pound, 60-pound, or 80-pound bags. Mixing bags on-site can become difficult if you’re pouring a large slab or have many footings.
Using bags can be easier than ready-mix when you have many small pours or a small project where a truck is not practical or cost-effective.
For the most part, ready-mix concrete from a truck is more cost-effective than bags and makes sense if you have a mid-size project and can pour all at once.
Calculating bags is a little less straight forward since each bag size will fill different volumes. Check the bag you’re using to find the exact fill-rate for the product. The table below shows the average fill for various pre-mix bag sizes.
|Bag Size||Pre-mix Bags Needed to Fill|
|1/4 cu yd||1/2 cu yd||3/4 cu yd||1 cu yd|
|40 lb bags||23||45||68||90|
|60 lb bags||15||30||45||60|
|80 lb bags||12||23||34||45|
How to Estimate Concrete Installation Cost
Ready-mix concrete typically costs around $115 per cubic yard, and pre-mix bags usually range from $2.50 to $7. Consider that for smaller projects there will likely be additional fees for ready-mix, such as delivery or short-load fees.
|ready-mix:||$115 per cu yd|
|pre-mix 40 lb bags:||$2.50 – $5 per bag|
|pre-mix 60 lb bags:||$3 – $6 per bag|
|pre-mix 80 lb bags:||$4.50 – $7 per bag|
The average cost to install a concrete slab is $6 – $20 per square foot. In addition to the cost of the concrete itself, there are also labor costs for preparing the area, the pour, and the finish.
A standard brush finish will likely be on the low end of the price range, while a decorative finish with coloring will be on the high end of the range. Consider getting a professional concrete installation estimate from contractors in your area for a more accurate cost estimate.
Preparing to Pour Concrete
Much of the work to pour concrete is done before the truck even arrives at the project. The site must be measured and laid out. Forms must be installed to create the edges of a slab or contain a footing.
Rebar or fiber or steel mesh should be installed to reinforce the concrete and to prevent cracking in the future. Try our rebar material calculator to estimate the amount of reinforcement needed for your project.
Make sure the installation team is ready for the installation and able to begin as soon as the truck arrives to avoid having it set up before the project can be completed and minimize idle time.
Tips For Ordering Concrete
Call your concrete supplier and ask them to advise you on the proper mix given your application and region. They should be able tell you what will work best to support the strength requirements and freeze/thaw cycles in your region.
Consider additional costs for a ready-mix delivery. Typically, there are fees for delivery, weekend service, small loads, and overtime for long unloading times. Call your supplier and understand these costs ahead of time and plan accordingly.
Order additional concrete for your project. The amount of overage you plan for will vary based on your quantity but plan for at least 10% overage to accommodate spillage, settling, and grading inconsistencies. This will save you from a bad pour in the event that your estimates are even slightly off.
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- Family Handyman, How to Estimate a Concrete Order, https://www.familyhandyman.com/masonry/pouring-concrete/how-to-estimate-a-concrete-order/
- Juan Rodriguez, Ready Mix Concrete Ordering Tips, The Balance, https://www.thebalancesmb.com/ready-mix-concrete-ordering-tips-844454
- On The House, Buying Concrete – 12 Tips to Determining Project Success, https://www.onthehouse.com/buying-concrete-12-tips-determing-project-success/