One of the most common questions for concrete projects is “how much concrete?” For most plans, the answer comes as a certain number of bags of mix. A standard bag of concrete comes in denominations of 20 – 40, 60, and 80 pounds are all common.
Because it sounds like a lot of concrete, people will often overestimate the coverage they think they’ll get. To visualize the proper amount in a standard bag of concrete, it’s good to think about using it in a real-world project. Whether you’re mixing it at home or having our team do the work, the first step is figuring the volume of the space you want to fill.
Calculating The Cubic Feet Of Your Concrete Project
The amount of concrete needed for most jobs is best expressed in cubic feet. The way to find the volume of a cube is to multiply the width, depth, and length. If your project were a perfect cube that was three feet wide, three feet long, and three feet deep, the volume would be 27 cubic feet.
However, most concrete slabs are not perfect cubes, making the math a little more complicated. A slab that is three feet long and three feet wide might have a depth of four inches, which is standard for most concrete surfaces. Your equation will look like this: 3’ x 3’x 4”. The problem is that everything has to be in the same units, and you can’t multiply feet by inches; instead, multiply 3 x 3 x 4 and divide by 12 (there are 12 inches in a foot). This project would need three cubic feet of concrete.
How Much “Yield” Will A Standard Bag Of Concrete Give?
For simplicity’s sake, let’s say you need only three cubic feet of concrete for your project. How many bags will you need? On a standard bag of concrete, you will find the cubic feet the bag will fill. This is the bag’s “yield,” and this number will act as the proper coverage for your home project.
The yield of most concrete mix is roughly 0.15 cubic feet for every 20 pounds of mix. This means that a standard, 60-pound bag has a yield of 0.45 cubic feet, while an 80-pound bag yields 0.60 cubic feet. To figure out what you’ll need, multiply the yield by the cubic feet of your project; in our hypothetical project, that’s three. To have enough concrete for this project, you would need at least two 80 pound bags (3 x 0.60 = 1.8, rounding up to 2).
But all construction projects have a margin of error, meaning it’s good to buy more concrete than you think you’ll need. If you’re doing the project yourself, purchase 10 percent more than your calculations show; you can return any unopened bags or save the mix for the future!