The maximum blood alcohol concentration the law allows for driving.

"BAC" means blood alcohol concentration: the amount of alcohol in a person's bloodstream, usually measured as a percentage. "Legal limit" means the cutoff where driving becomes unlawful based on that number alone, even if the driver does not seem obviously drunk. In Washington, the main adult limit is 0.08 under RCW 46.61.502 (2024). The limit is 0.04 for many commercial drivers, and drivers under 21 can face penalties at 0.02 under RCW 46.61.503 (2024). A person can still be arrested or charged below those numbers if alcohol or drugs made them unable to drive safely.

That number matters because it often becomes the centerpiece of a DUI case. Police and prosecutors use breath test or blood test results to argue that impairment was illegal per se. Defense lawyers may challenge how the test was given, whether the machine was maintained, whether the stop was lawful, or whether rising BAC affected the reading.

In an injury claim, a BAC over the legal limit can strongly affect liability, settlement value, and insurance negotiations. If an impaired driver caused a crash during heavy rain, hydroplaning conditions, or a sudden visibility problem, intoxication can still make fault much harder to defend. If the injured person was the one over the limit, comparative fault may reduce what they can recover.