How to Calculate Cement Slabs

A patio can add more functional living space to a home.

Cement patios can add character, charm and additional living space to the outside of a home. Many homeowners choose to save a bundle of money by pouring the patio themselves using ready-mix concrete that they add water to. Before you begin the project you'll need to determine how many bags of ready-mix concrete you'll need for your size patio.

Instructions

1. Measure the length and width of the area you want to cover with cement. For example, you might want to build a patio in your backyard measuring 10 by 18 feet.

2. Multiply the length and width you found in Step 1 by each other. In the example, 10 feet times 18 feet is 180 square feet.

3. Multiply the answer from Step 2 by one third of a foot to find the volume of the concrete slab. Patios are generally 4 inches deep, which is one third of a foot. One hundred eighty square feet times one third of a foot is 60 cubic feet.

4. Divide the answer from Step 3 by two thirds. An 80-pound bag of ready-mix concrete fills two thirds of a cubic foot. Sixty cubic feet divided by two thirds is 90 bags of concrete.

Tips & Warnings

• Some specialty types of concrete such as structural concrete used on elevated decks have different volumes, so check the front of your concrete bags and adjust the divisor in Step 4 if necessary.

References

• Portland Cement Association: Basic Concrete FAQ