What is Blood Alcohol Concentration?

You must be below 0.05% BAC to drive in Australia, and professional drivers are generally required by law or company policy to have zero blood alcohol [1].

Alcohol slows your reaction time, impairs your judgement and decision-making, and gives you a false sense of confidence – at a BAC of .05, your risk of being involved in a road crash is approximately double compared with a BAC of zero [2].

Blood Alcohol Concentration (BAC) measures the amount of alcohol in your bloodstream. A BAC of 0.05% means that for every 100ml of blood, there is 0.05g of alcohol [3] [4].

This fact sheet explores the science behind how your body absorbs and metabolises alcohol to help you understand how fast your body can break down alcohol and how long after drinking your BAC will remain elevated.

How the body processes alcohol

Alcohol is a depressant (a substance that reduces arousal and stimulation) and has a short life span in the body.


Alcohol is swallowed and enters the digestive system to travel to the stomach and small intestine. Approx. 20% of alcohol is absorbed through the stomach, and 80% through the small intestine, and directly to the bloodstream.

When alcohol enters the bloodstream, it is transported throughout the entire body. Blood circulates through the body in an average of 90 seconds, allowing alcohol to affect the brain and other organs rapidly. The full effects of the alcohol are felt within 15-45 minutes.


Most of this alcohol ends up in the liver, where metabolism takes place as the liver releases enzymes that break down the alcohol.

In general, the liver can process approximately 10g of alcohol (one standard drink) per hour. If you’ve consumed more than one standard drink, the system becomes ‘saturated’, and the excess alcohol accumulates in the blood and other tissue until it can be metabolised.

To read full fact sheet download PDF below.