Hi I am building a garage, and am doing the base at the moment. The base size is 5.7 x 3.3 mt, and am looking to having 4 inch of concrete. A retired builder friend of mine worked out that I would need 2 tons of ballast, and 18 bags of cement (5 to 1 mix ). This worked out woefully short on the ballast. I wonder if he was working in cubic yards and imperial tons. I got the ballast from a yard with a weigh bridge, I am presuming nowadays I would have brought metric tons. I would just like to know for future reference how it should have been worked out. Can somebody help me out here please.