You can't mandate a fixed code/comments ratio otherwise you finish up with code laced with noise like:
// Add one to i
i++;
which just clouds the code.
Instead look at the complexity of the code and see what you need to explain, i.e. squirelly logic, why certain magic numbers are used, what assumptions are present regarding incoming formats, etc.
Switch on your maintainers mindset and think what would you like to see described regarding the code you've just written.
HTH.
cheers,
Rob
