1 Answer

Well, it depends upon your use of the slab. Customarily, a slab that will only have to endure foot traffic is poured only 4 inches deep, While a slab that will have to endure automobile traffic is usually poured 6 inches thick. For 6 inches thick it is 20x20x.5=200 cubic feet of concrete. For 4 inches thick it is 20x20x.33= 132 cubic feet of concrete. The formula is width x length x height for the volume of whatever you'll need. Next, you should consider re-bar or reinforcing wire that you will pour your concrete over. The is to strengthen your slab. You will have to screed and trowel it also. You might want to mull over the possibility of creating a slight slope for drainage purposes. There is nothing worse than a slab of concrete that holds puddles, it sort of otherwise defeats the purpose of a well poured slab.