It depends on your interior color. My front is 20% to match but it looks darker than that because my interior is blacked out and I have a black suede headliner. I finally got my first tint ticket ever last week. Driving slowly in the pouring rain in traffic when I see blue lights. Of course it's a young rookie cop who has his tint meter in hand. Asks me if I can even see out of my car and if I've ever been written a tint ticket. I say no and he seems surprised and proceeds to write the ticket. Of course in pulling me over, he ignored the guy right in front of me who ran the red light. Then after picking up my son from school, I come back down the road the other way not even 5 minutes later and he has someone else pulled over. Must have been trying to hit his quota.
Oh well, that's the price of having stuff out of compliance. I actually was pulled over last year and the officer checked the tint and told me it was illegal, but it was above his "personal" limit for a ticket so he let me go after checking my license. Win some lose some.