Calculate the number of cubic yards of concrete by calculating the volume of the pour and adding 10 to 15 percent to ensure you have enough material. If you calculate volume in cubic inches or cubic feet, use a conversion factor to convert the volume to cubic yards.
Calculate the surface area of the project by measuring the length and width and multiplying them. If the project is not rectangular, use graph paper, and draw the surface. Divide it into smaller rectangles, and calculate the area of each. Then, add the areas together. For large projects such as driveways, it is usually easiest to measure length and width in feet. Convert any remaining inches in a measurement to a fraction of a foot by dividing them by 12. Convert the depth of concrete into feet, and multiply the surface area by the depth of the concrete.
To convert cubic feet to cubic yards, divide by a conversion factor of 27. This is the number of yards the pour requires in a perfect world. Often, irregularities emerge in the depth or form for the concrete, so add on an extra 10 to 15 percent when making your calculations. Having to order a second truck of concrete for less than a yard of concrete often involves a significant surcharge.