Ready mixed concrete is ordered by the cubic yard. One cubic yard of concrete equals 27 cubic feet — or the amount of concrete that would fill a container that is 3 feet wide X 3 feet long X 3 feet deep. To determine the amount of concrete for your specific project, calculate the in place volume - in feet - by first multiplying the length by the width, which will give you the total square feet or surface area. Then, take that number and multiply it by the depth or thickness of your pour, also in feet; keeping in mind that 4 inches is equal to .333 feet. Next, divide that number by 27 (the number of cubic feet in a cubic yard) to get cubic yards. Which means that the amount of concrete you would need to pour a slab that is 20 feet by 24 feet and 4 inches thick would be a little less than 6 cubic yards:
20 (ft) X 24 (ft) = 480 square feet X .333 (ft) = 159.84 cubic feet
159.84 cubic feet divided by 27 cubic feet (1 yard) = 5.92 cubic yards
Of course, depending upon how accurate you were able to measure things, how uneven the bottom surface of your project area might be, how much space any pipes or columns or reinforcing materials might occupy, and how much might be spilled during placement, actual amounts will vary. And, there will almost certainly be some amount of waste. So be sure to make any needed allowances and consider ordering a little extra to compensate. Assuming that an additional "short load" could be scheduled in time, the extra delivery costs and finishing delays could prove to be quite costly.
Depending upon roadway weight limitations en route to your project and the type of concrete being placed, a single Molalla Redi Mix Truck is able to haul up to 10 or 11 yards of concrete per trip. For large projects, several truck loads can be scheduled at the same time or in succession; whichever approach best meets the requirements of your specific project.