I know in NY (home state) you can not go darker than 35% on the passenger/drivers doors.
Tom is right with the computations, which means you can not go lower than 35 % for the front two side windows.
Rear door windows and rear window you can go dark as you want. Limo is insane, 5 % is even crazy. I had 5% on my back 3 windows years ago..... could not see out them to back the car up at night, would have to roll the window down and use side mirrors... Pain in the a$$. Suggest not darker than 15%, but my choice is 20%.