Ready-mixed cobcrete is sold by volume measured in cubic yards. If you can determine the area of your concrete project (lenght x width for rectangular projects) and know the tickness of the slab, you can use the information in the table below to determin how much concrete you need.

For example, let's calculate how much concrete is needed for a 5-inch thick rectangular driveway, 60-feet long (lenght) and 18-feet wide (width). The area of driveway is 1,800 square feet (60-feet x 18-feet). According to the table above, one cubic yard of concrete placed at a thickness of 5-inches covers 65 aquare feet. In a perfect world, our 1,80 square foot driveway will need exactly 16.62 cubic yards of concrete (1,080 square feet / 65 square feet equals 16.62 cubic yards).

But Job sites are not pefect, and batch plants cannot produce concrete to such exact volumes. To allow for spillage during placement, form movement, uneven subgrade, and consolidation, most contractors order 10% to 15% more concrete than the computed volume for the forms, and round up to the nearest quarter yard. In our example 16.62 cubic yards x 115% = 19.2 cubic yards. Rounded up to the nearest quarter yard, we would request 19.25 cubic yard of concrete when ordering concrtete for the project.