Blood alcohol concentration (BAC)
Blood alcohol concentration (BAC) is the amount of alcohol in the bloodstream. A BAC of 0.05 means the person has 0.05 grams of alcohol in every 100 mL of their blood.
As the liver metabolises alcohol at a rate of about three-quarters of a standard drink per hour, the BAC drops over time, unless more alcohol is consumed.
BAC is measured with a breathalyser, or by analysing a sample of blood.
Factors affecting your BAC
The more a person drinks, the higher their BAC. However, 2 people who drink the same amount might register quite different BACs. This is due to a range of factors, including the following.
Body size
A smaller person will have a higher BAC than a larger person because the alcohol is concentrated in a smaller body mass.
Empty stomach
Someone with an empty stomach will reach a higher BAC sooner than someone who has just eaten a meal. Food in the stomach slows down the rate at which alcohol passes into the bloodstream.
Body fat
People with a lot of body fat tend to have a higher BAC. Alcohol is not absorbed into fatty tissue, so the alcohol is concentrated in a smaller body mass.
Sex
After consuming the same amount of alcohol, a female will almost always have a higher BAC than a male.
Because of all these variable factors, counting the number of standard drinks you consume can give only a rough guide to your BAC.
For more information, please click on the Australian Drug Foundation's DrugInfo Clearinghouse web site link below.
Last Reviewed: 20 September 2006
