I am looking for the formula for the different sized boards for the joist (ex. 2 X 6, 2X 10) The formula that I am looking for is how to calculate the maximum span I can run my floor joist using a deflection of L/360. and I am also looking for the spacing between joist. I am not sure what a good pounds per square foot would be, I am not putting a hot tub or anything on the deck. I know there are places on line that I can enter the type of wood I am using but in the size of board I want to use and specify the spacing that I would like to use and it will calculate the span that I should not exceed. But I am looking for the formula that is used to arrive at that answer if anyone can help me out.