Pouring Concrete: Calculating How Much Concrete You Need

A Formula to Help When Pouring Concrete Footings, Etc.

Builder pouring concrete into house foundations
Simon Battensby/Photographer's Choice RF/Getty Images

There is a very simple way to figure out how much concrete you need when pouring concrete. Like many construction materials, concrete is measured and sold in cubic yards. In the construction industry, you will hear people talking about how many yards of concrete they need, or how many yards they poured. With a few measurements and some simple math, you can figure out how many yards of concrete you need for your project.

Of course, when the word, "math" rears its ugly head in a discussion, the last word that comes into the heads of some folks is "simple." Never fear: I have provided the formula that you will need to work with below, so that all you need to do is to plug in some measurements. I even offer examples to further allay the fears of the truly mathophobic.

Formula to Use to Calculate How Much Concrete You Need

Do not be afraid of math formulas: they are actually intended to make your life easier, taking the guesswork out of things like buying the correct amount of concrete for a project. Have a look at this formula (doing so will not singe your retina -- I promise!):

(L'xW'xH') / 27  = cubic yards of concrete needed

OK, I'm sure that even those suffering from mathophobia survived taking a look at the formula. But now, what does it mean, exactly?

Example Showing How to Use the Formula

Let’s do an example to demonstrate how the formula works.

Let’s say we’re pouring a concrete footing for a mortared stone wall. To determine how much concrete we need, we will use the formula above. According to the formula, we need three measurements:

  1. The Length, measured in feet
  2. The Width, measured in feet
  3. The Height, measured in feet

Note: The apostrophes after the L, W, and H indicate "feet." This is shorthand used by carpenters and others in building trades.

To indicate inches, you would use quotation marks. Thus 15" means 15 inches.

We’re going to multiply all three of these numbers together. Then, we will divide that number by 27 to see how many cubic yards of concrete we need. 

For our example, let’s say our footing will be 20 feet long, 2 feet wide, and 1 foot high.  Let’s do the math:

                                                20x2x1 = 40

Now divide by 27:

                                                40/27 = 1.48 cubic yards of concrete

Does that make sense?  For pouring concrete footings 20 feet long, 2 feet wide, and 1 foot long, you would need 1.48 yards of concrete.  When talking about concrete, people usually drop the "cubic" and just say "yards," so do not be confused if the person who takes your order when you are ordering the concrete fails to use the term, "cubic."

If I were having this concrete delivered on a concrete truck, I would order 2 yards.  It is always better to have a little extra than to run short; let's call it the Better Safe Than Sorry rule. The same holds true for ordering many other landscaping supplies; for example:

  1. Stone dust
  2. Paving stones
  3. Compost

Occasionally, you might decide to make an exception to the rule.

For example, if the color of the mulch you use is important to you, you may wish to avoid ordering too much excess bark mulch, because its color fades over time. So in that case, you'd want to order pretty much the amount that you think you will be using immediately.