Joe: Figure most concrete slabs are 4 inches thick. One cubic yard of concrete is 81 square feet at 4 inches thick. Take the previous dimensions of your patio and figure from there and that should put you in the ball park as far how much concrete you have. The dumpster is a different matter all together. You will max the dumpsters weight capacity at about 1/4 to 1/3 of it's cubic capacity with all that concrete.