Calculating how much concrete you’ll need for a project comes in two steps. The first step is determining what kind of concrete you will need. There are many, many kinds of concrete out there. Mixed concrete can be complex, meaning it can be really strong or not. Modern or regular concrete is a mixed design using sand and other common materials that withstand pressure pretty well. Some concrete is known as high or ultra-high performance, meaning they can really take any kind of hit. Then there’s cellular, cork, roller-compacted, glass, asphalt concrete types—endless possibilities to choose from. Talk to a concrete specialist to see which is best for your project.
After you pick the material, you will need to figure out exactly how much of it you will need for your concrete project. All concrete is estimated in cubic yards (one cubic yard = 27 cubic feet). For large concrete jobs—four cubic yards or more—the concrete should be delivered by ready-mix truck. It’s also possible to haul fresh concrete to your site in special two-cubic-yard trailers provided by concrete producers. For small or medium jobs, it’s best to mix your own in a rented concrete mixer. For very small jobs, you can purchase sacks of ready-mix that only require you to add water.
The best way to calculate how much concrete you’re going to need in cubic yards is to do the following:
- Mark the area that will need concrete and divide it into smaller areas.
- Calculate its volume of the area after determining the shape of the area (see chart below) by multiplying in the height.
- Convert the volume from feet to cubic yards to get the number of cubic yards of concrete you’ll need.
Foundation walls and stem walls with footing will require different calculations than anything in the chart. Foundation walls will be thicker and therefore require more concrete to stay strong against a whole house atop them. Calculating them will require the thickness, length of the wall and footing, height and width of the footing and wall, along with the thickness of the footing. For stem walls, calculate the footing area, the wall and add them together.
|Multiply length by width.||length, width|
|Square the circles radius; multiply by 3.1416.||diameter|
|Halve the base length; multiply by height. Or, multiply the base length by the height and divide by 2.||base length, height|
|Square the short diameter; multiply by .866.||short diameter|
|Square the short diameter; multiply by .828.||short diameter|
|Draw the project out on graph paper, with 1/4 inch representing 1 foot. Count up the number of squares. Partial squares count as one.||length, width|