Legally, you are considered to be driving under the influence if you have a minimum blood alcohol content (BAC) of:

Drivers age 21 and older are considered to be driving under the influence (DUI) if their BAC is 0.08 percent or greater. If a person's driving is impaired, they can be convicted of a DUI even if their BAC is lower than 0.08 percent. Drivers under age 21 can be convicted of illegal consumption of alcohol if their BAC is 0.02 percent or greater.
DMV Writen Test