How many yards of concrete do you need for a 12' x 12' x 3 slab?

Answer 1

1.33 cubic yards, but that should be rounded up to 1.5 cubic yards. I would recommend going to 4 inches and if you are in a colder climate ordering that as a 4,000 psi mix, with air entrainment, set at a 6 inch slump at the plant using a low range water reducer. If you want to play with the thickness, then there is a related link to a calculator below.