Things You'll Need
Many different projects around the house require the use of concrete. Whether you're setting fence posts or building a new patio, concrete is the material of choice to provide a durable product that will last for years. Concrete is sold by volume and must be calculated this way to provide a proper estimate of the material needed. The standard unit is the cubic yard. Although some may find a concrete takeoff daunting, the process is straightforward with a little knowledge and the right tools. Below is an example for a rectangular patio, but the same principle holds true for any concrete takeoff.
Outline the area where you want the concrete to go. This can be done on paper or at the installation location. If you perform this on paper, include dimensions of the area or draw the structure to scale.
Measure the structure's length and width, and write these measurements on the paper. Make these measurements in feet for ease of use. Make all measurements to the nearest inch.
Convert inches to feet. Take the inches from the length measurement and divide it by 12. Add this number to the number of feet for the length and use this as your length measurement for future calculations.
Calculate the surface area of the structure. Do this by multiplying the length by the width. Write down this number as the area in square feet.
Determine the depth of the structure. Most flatwork, such as patios, driveways and sidewalks, are about 4 inches.
Convert the depth to feet. If your depth measurement is in inches, divide it by 12 and write down the result. This is your depth measurement for future calculations.
Calculate the volume of the structure. Multiply the surface area by the depth. Write down the product. This is the volume of the structure in cubic feet.
Convert cubic feet to cubic yards. Divide the cubic feet product by 27 to convert to cubic yards. Most concrete supply companies sell their concrete by the cubic yard. This number will be useful.
Order additional material for waste. As a general rule, 10 percent is used as the waste amount, so multiply your final amount by 1.1 to allow for waste.