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How to Estimate Your Concrete Job

Working with concrete can create a bit of anxiety, no matter how big or small the job—whether you’re placing a slab, leveling out a space for a patio or setting posts. The first and most important step for any concrete project is to work out the volume of concrete needed – which isn’t always easy, even for pros who are used to working in cubic yards.

That’s where Dirk Tharpe, Sakrete’s go-to concrete expert and affectionately known as the Carolina’s Concrete Cowboy can lend a hand with an easy way to estimate any project. Tharpe handles sales and training for Sakrete, Oldcastle APG’s brand of time-saving, pre-blended, bagged building materials and concrete.

“Estimating a cubic yard of Sakrete concrete is easy,” said Tharpe. His 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 great method to get a good 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,” said Tharpe. In other words, 1 cubic yard of concrete placed at 4-inches deep will cover 81 square feet.

Alternate Method

Alternately, one pallet of 56, 60-pound bags of Sakrete mix is also close to one cubic yard of concrete. Again, it actually takes 4 additional bags of 60-pound mix to equal a full cubic yard. But, this is a helpful estimating process.

The formula for estimating the volume of concrete in cubic yards needed on a project is straightforward, though it will require a calculator.

Simply multiply the length by the width by the depth of the desired slab in inches, then divide by 1728. 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. (See Tharpe’s YouTube on Estimating Cubic Yards at www.youtube.com/watch?v=ifJ1itcmHs8&t=)

Another shortcut method requires knowing a little about how far a single bag of concrete will go. The trick: for each foot of concrete, you’ll need 1 50# bag, .8 60# bags or .6 80# bags. 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.