How do I know if Im ordering the right amount of concrete?
This is a great question and one that is mathematically easy to answer. However, in the real world of construction, someone always comes up a yard short and the agony begins for the concrete dispatcher who is short on available trucks as well as the finishing crew that has six guys standing around. To determine how much concrete you need, simply multiply length x width (square footage) x depth (cubic footage). A 20 x 20 slab, five inches thick equals 400 square feet or 168 cubic feet (20 x 20 x .42). Since there are 27 cubic feet in a cubic yard of concrete, divide 168 by 27 to get 6.2 cubic yards. This is where things get interesting. Most commercial contractors add anywhere between five and 10 percent for grade variations and then order their concrete. The difference between five and 10 percent on the above example is the difference between 6.5 yards and 7 yards. Many who have come up the proverbial yard short claim their pour was exactly on grade. That is often a point of contention
