Blood Alcohol Content (BAC) Calculator

Blood Alcohol Concentration (BAC) is a percentage that indicates the amount of alcohol in your blood. A BAC of 0.08% means there are 0.01 grams of alcohol per milliliter of blood. This calculator estimates your BAC based on gender, weight, drink consumed and time of drinking.

It also shows how you would normally feel at that concentration, whether the legal limit has been exceeded and how long it takes to get back down to zero. All values are estimates and should never be interpreted as a licence to drive.

How to use the calculator:

The Widmark formula is used for the estimation, a model on which most BAC calculators are based. It distributes the amount of pure alcohol consumed across body water and subtracts the amount already metabolized by the liver.

where A is the amount of pure alcohol in grams, W is weight in grams and r is the distribution coefficient reflecting average water content in the body; it is about 0.68 for men and 0.55 for women. The term 0.015 gives the rate at which the BAC decreases per hour as the body eliminates alcohol, and t is the time elapsed since the first drink.

For example, a man who weighs 154 pounds (about 70 kg) drinks three standard drinks in one hour. Since three standard drinks contain 42 grams of alcohol, the peak level is (42 multiplied by 100), divided by (0.68 multiplied by 70,000), which is about 0.088%. An hour after drinking, his blood alcohol content will be around 0.073%, just below the common limit of 0.08% but still close enough that another drink would put him over the limit.

What is a standard drink?

A standard drink does not refer to a specific volume of liquid, but rather a defined amount of pure alcohol. In the United States this is 14 grams, so for example both a small high-alcohol drink and a large low-alcohol drink can each count as one standard drink.

If a drink has more than the standard amount or has a higher alcohol content, use the per item mode and enable custom drinks. Enter the exact quantity and alcohol content to calculate the amount of alcohol in that drink with an integrated calculator.

What does BAC stand for?

The following effects are typical for people with lower tolerance; the effects can vary widely at the same BAC level depending on whether a person drinks heavily or only occasionally. Regardless, however, driving and health risks increase as the number goes up.

Legal blood alcohol limit for driving.

In most regions of the United States, it is illegal to drive a vehicle with a blood alcohol concentration (BAC) level above 0.08%. For commercial drivers, the limit is lower at 0.04%. Drivers under the age of 21 are subject to zero tolerance laws, which generally set limits between 0.01% and 0.02%. In most European countries, the limit is 0.05%, while some countries have a 0.02% or zero tolerance law.

A calculator allows you to set your personal limit and receive location-based warnings when it is exceeded. Bear in mind that the effects of alcohol can be felt below these limits so being within the legal range does not necessarily mean you are safe.

Factors that affect actual BAC include:

The Widmark model uses averages and may not reflect all of your individual circumstances. Eating before or while drinking slows the absorption of alcohol into your blood stream and lowers peak levels. Also, because alcohol is distributed in water but not fat, your body composition plays a role.

Medications, health conditions, the speed of alcohol consumption and even mixing with carbonated drinks can affect actual readings. So people who drink the same amount may have different final BACs, and the actual number could be both higher or lower than the estimates given here.

How long does it take for alcohol to be broken down?

The body processes about one standard drink per hour or reduces blood alcohol content (BAC) by about 0.015% at a relatively constant rate. Because this rate is fairly consistent, it's possible to still be over the limit in the morning after drinking heavily overnight.

There is no way to speed up this process. Coffee, a cold shower, a nutritious breakfast or exercise may make you feel more alert but they do not lower your BAC. Only time can lower your BAC. So the calculator shows how many hours it will take for you to be below the limit and when your BAC will be zero again.

Used symbols:

This calculator is for general educational purposes only and does not constitute medical or legal advice. The results are estimates and may vary significantly from actual values, so they do not replace breathalyzer tests or blood tests. The safest amount of alcohol to drink before driving is zero. If you have concerns about your drinking habits, please consult a doctor or addiction specialist.