oncrete is measured in cubic yards. first measure depth ie. 6’= 1/2 ft etc. then width and length. make sure all measurements are the same units, feet are easiest. then convert to yards. example is 6′ deep by 10 feet wide by 20 feet long is figured by the following: 1/2 X 10 X 20 = 100 cubic feet divided by 36 for cubic yards = 2.8 cubic yards or just ‘yards’. usually rounding up to 3 yards for delivery. Remember you have your local hardware stores that would love to help you as well. Happy Building.