"How stoned is too stoned to drive? In other words, what is the legal limit?
You are considered to be under the influence if you have a THC concentration of 5.00 or higher as shown by a blood test. You also could be arrested for driving under the influence if an officer believes you've been affected by marijuana use. Even if your THC level is under 5.00, you still could be arrested if you've used marijuana in combination with alcohol or another drug.
Learn more online by looking up RCW 46.61.502."
From an article in the Bellingham Herald. No idea what the numbers represent.