Multiply figures for length, width and thickness, measured in feet, and divide by 27 to determine the yardage of concrete required. Multiply the total yards by 1.05 to allow for a margin of error to ensure enough materials are available. With a pocket calculator and tape measure, the process takes only a few minutes.
- Measure the project
Use a tape measure to determine the size of the project. Enlist a helper to hold one end of the tape. Record the measurements in feet. Convert any inches over the full foot measure to a fraction of a foot by dividing the remaining inches by 12. Measure and record the dimensions of any areas that lie outside the larger rectangle in a similar method.
- Multiply to find volume
Convert the thickness of the concrete to a fraction of a foot. Calculate the volume by multiplying length by width by depth. Add any additional volumes from out of the main rectangle.
- Convert to cubic yards
The volume figured using measurements in feet provides the number of cubic feet. Divide the volume by 27, the number of cubic feet in 1 cubic yard.
- Include overage
Multiply 1.05 by the number of cubic yards provided for over-excavation, spills and unforeseen events. Many concrete companies have a minimum load size or an additional charge for small loads, making it less expensive to have a small amount of materials left over than to have to order more concrete.