5% on back window
50% or 35% on back windows
50% on front windows (I'm in Michigan)
50% front windshield (not sure about this)
I'm mainly going for heat reduction rather than privacy, except for the backwindow. I want total privacy from the back so people/drivers can't see inside my truck when driving behind me.
With that combo your gonna have a hard time backing up at night, but people will still be able to see in, a least a little, during the day.
I have 45% windshield, 15% on top of 20% on the front two windows, and 15% on all of the rear windows, which also had factory tint. Even with that combo you can SLIGHTLY see through the back during a sunny day. By slightly I mean that it has to be really sunny and the average person probably wouldn't notice, but I do.