There are many factors that can influence your blood alcohol concentration (BAC) when you consume alcohol. You can measure your BAC with a fully calibrated testing machine. But can you estimate it? For the most part, no. There are way too many variables that come into play. The only time you can accurately estimate your BAC is when you have had no alcohol to drink. Not drinking is the safest option if you're driving. But if you're going to drink, play it safe, plan ahead and find an alternative