According to the Washington State law, the maximum tint allowed for car windows is 24%. The darkness of the tint is measured by the amount of light that passes through the window glass with film installed. The percentage of light allowed through your film and glass in Washington is very specific and different for cars and SUV/vans. Here are the details:
Windshield: Non-reflective tint is allowed, only on top 6 inches of the windshield.
Front Side windows: Must allow more than 24% of light in (Film+glass).
Back Side windows: Must allow more than 24% of light in.
Rear Window: Must allow more than 24% of light in.
SUV/vans are allowed darker windows behind the front 2 doors with almost no restriction.
Complete windshield film is NOT legal in Washington state.