Wow.....you're a lot of help.
Instead of guiding him, you push him off the edge of a cliff.
There are thousands of variables that can affect the size or type of steel needed. You failed to mention how it will be used. Is it attached at the pivot point of a lever or slightly offset?....how much weight on the lever, in static and in a dynamic state. What is the length of the lever???
What are the constraints you have to work with?
Torsional stress= length of lever(inch) x weight. So 12 inch lever multiply's the weight at the fulcrum 12 times (Torsional stress) if bar is placed at pivot of lever.
People here would gladly help you if only you would give them a fighting chance, by giving them some specifics.
Oh and BTW, There are many free online calculators.
Good luck with your project......