How to Estimate Concrete for a Project
Concrete is one of the most prevalent residential building materials, whether you’re placing a slab, leveling out a space for a patio, or setting posts for a deck or fence.
Concrete Delivered by Truck
For large projects such as a long driveway, fresh concrete professionally delivered by a truck is usually sold by the cubic yard. To determine the volume required, you’ll need a calculator. Multiply the length by the width by the depth of the desired slab in inches, then divide by 1,728. The result is the total cubic feet of the slab. To get to cubic yards, divide that number by 27. It’s also a good idea to add ten percent to adjust for variations and waste to get your final number.
Bagged Concrete Mix
When it comes to calculating the amount of bagged concrete required, we turn to Sakrete’s concrete expert, Dirk Tharpe, who handles sales and training for Oldcastle APG’s brand of time-saving, pre-blended, bagged building materials and concrete.
Tharpe’s rule of thumb: One pallet containing 42 bags of 80-pound Sakrete High-Strength Concrete Mix is about a cubic yard of concrete. Though it actually takes 45 bags of 80-pound mix to hit a cubic yard dead-on, this is a good method to get an initial estimate.
Visualizing how far a cubic yard goes isn’t always intuitive either, but Tharpe has a solution. “Think of a 9’ x 9’ slab at 4” deep, or about five sidewalk squares,” says Tharpe. In other words, 1 cubic yard of concrete placed at 4-inches deep will cover 81 square feet.
Alternately, one pallet of 56, 60-pound bags of Sakrete mix is also close to one cubic yard of concrete. Again, it actually takes four additional bags of 60-pound mix to equal a full cubic yard but this is a helpful estimating process.
Another shortcut method requires knowing a little bit about how far a single bag of concrete will go. The trick: For each foot of concrete, you’ll need 1-50# bag, 0.8-60# bags or 0.6 80# bags. Although this method only works with a 4” slab, it’s a single calculation that also automatically works in the 10% waste factor, making it a great standby.
For example, if you have a 9’ x 9’ slab at 4” deep, you have a total of 81 feet. If you’re using 80# bags, you multiply the total feet (81) by the .6 bags per foot trick to get 48.6 bags – a bit on the high side, but in concrete it’s always better to be safe than sorry.
“While there is nothing wrong with traditional estimation, it’s definitely not something most of us can do in our heads!” says Tharpe. “Plus, not all jobs are easy rectangles. Adding concrete footings to posts or laying an irregularly shaped or curved slab can require meticulous measuring, or make you dust off your old geometry book, and that can slow you down … but as they say, we have an app for that!”
Concrete Calculating App
Tharpe describes Sakrete’s free estimating app as not just a measuring tool, but a total volumetric job estimator. Ideal for novice DIY’ers or seasoned pros, the app features simple point-and-shoot estimates on a smart phone without the hassle of tedious calculations. It eliminates the guesswork and helps keep the project on track from start to finish.
Estimating the necessary volume of concrete with the app is very intuitive. Start by choosing a project type, then enter the project’s dimensions using the app’s Augmented Reality (AR) function to scan the area to receive the recommended Sakrete product, quantity and where to buy it locally. It can even estimate curves and irregular shapes with ease, simply by tapping the screen to place pins along the perimeter of the project area. The app also includes a tutorial for new users.
Completely free and available in English and Spanish, the Sakrete app can be downloaded for iOS and Android on the following devices: iPhone 6S or newer, iPad Pro (9.7”, 10.5”, and 12.9”), iPad 2017, or newer and Android devices running Android 7.0. Go to your app store or download at www.sakrete.com/app.
“Using AR spatial technology to measure and scan project sites, the app can quickly calculate the number of concrete bags needed for slab or post projects,” says Tharpe. “It’s an easy way to save time, money and material.” Learn more at www.sakrete.com.