Concrete Calculator How Much Concrete Do I Need? The ...
4 ÷ 12 = .33; 100 x .33 = 33 cubic feet; 33 x .037 = cubic yards; Essentially you are solving for volume and then converting to cubic yards. For concrete, the formula for volume is as follows: length x width x thickness. To determine how many bags of concrete you will need, divide the total cubic yards needed by the yield.