I have a cable 1.1 Inches in diameter. The National Electric Code says that a metal conduit cannot be filled more than 60%. It must have 40% of its space free. What size conduit should I use?

Not enough info to answer your question. What conduit type are you planning to use?

A quick and dirty answer is the largest you can especially if you have to pull the cable around any corners. I assume that due to the size that it is stranded. I personally would only think 2 inch or greater having pulled many miles of cable in my life.