If you are 21 years or older, you can only drive a car in California if your blood alcohol content (BAC) is less than .08%. If you are under the age of 21, you can only drive a car if your BAC is less than .01%. Be aware that you can also be in violation of DUI statutes if your driving is impaired by drugs or alcohol, no matter your BAC. Driving can be impaired at very low levels of alcohol consumption. We always advise not to drive if you have been drinking at all.