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Decorative Concrete Institute in Temple, GA

Decorative concrete patios come in all shapes and sizes. Some are basic rectangles, while others have curved or rounded configurations. Determining how much concrete you’ll need for a square or rectangular slab is fairly straightforward. But figuring out the amount required for an irregular patio shape is trickier.

To avoid mistakes, either on the plus or minus side, follow these basic rules for determining the quantity of concrete you’ll need for a patio slab. These apply whether you are ordering concrete from a ready-mix supplier or buying a bagged mix.

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## Determine the size of patio you need

The first step in designing your patio is deciding on a size and layout that fits your needs and space. Consider factors like the patio’s function, the number of people you plan to accommodate, and the size of the patio furniture you will be using. Get more tips for sizing a concrete patio.

## Measure the patio dimensions

Once you come up with a layout for your concrete patio, you’ll need to take precise measurements of the area to accurately figure out how much concrete will be required. Here are general guidelines for measuring patios of different configurations:

• For a rectangular or square slab, simply measure the patio length and width.
• To figure out the dimensions of irregularly shaped slabs, create a scaled drawing of the project on graph paper then divide the irregular shape into a series of rectangles to determine the area for each in the overall layout. Add the results of all your shapes to get the total area.
• For a circular slab, measure the diameter of the patio by taking its radius (the distance from the center of the circle to its edge) and doubling it.

When taking your patio measurements, make sure to exclude any areas that won't be made of concrete. For example, if the concrete patio has a brick border or is broken up by wide strips of grass or decorative stone, those areas should be omitted from your calculations.

## Determine the patio thickness

The thickness, or depth, of a concrete patio also factors into how much concrete the project will require.

Generally, a concrete patio is poured at a minimum thickness of 4 inches. However, if your patio will support heavy loads, such as a hot tub or outdoor concrete fireplace, you may want to increase that to 5 or 6 inches. Don't forget to check the local building codes, which may have minimum thickness requirements for a concrete patio.

## Calculate the cubic yards of concrete needed

Because ready-mix concrete is sold by volume, measured in cubic yards, you’ll need to determine the cubic area of your concrete project. The basic formula is to take the patio thickness converted into feet and multiply it by the width and length of the patio. Then divide the total by 27 to convert cubic feet to cubic yards. You can use our online concrete calculator to help you do the math.

For example, a 4-inch-thick concrete patio measuring 12 feet long and 12 feet wide will require approximately 1.78 cubic yards of ready-mix concrete or 81 80-pound sacks of bagged mix. (Each 80-pound bag yields approximately 0.022 cubic yards of concrete.)

To determine the cubic yards of concrete needed for a circular patio slab, the formula is a bit more complicated. You’ll need to multiply pi (3.14) by the radius in feet squared and the slab thickness in feet, divided by 27.

## Leave room for error

If you underestimate and don't buy enough concrete, you'll have to put your patio project on hold. To avoid this, order 10% to 15% extra concrete so you’ll have enough material to finish the job. This allows for possible errors and compensates for concrete spillage and an uneven subgrade.

In our patio example above, 10% x 1.78 cubic yards of concrete = 0.178, for a total yardage of 1.96. When you round up, you would need to order 2 cubic yards of concrete for your patio project.

## Should I use a bagged mix or hire a ready-mix supplier for my patio project?

An advantage of bagged concrete mix is that you can mix up another batch onsite if you come up short. However, ordering from a ready-mix supplier is a good way to go if you have any doubts about your patio measurements. They can often help you with your calculations, especially if you’re dealing with an oddly shaped slab.