BAC Calculator

What Is a BAC Calculator?

A BAC calculator estimates the amount of alcohol in your bloodstream after drinking. BAC stands for Blood Alcohol Concentration, also commonly called Blood Alcohol Content.

BAC is usually expressed as a percentage. For example, a BAC of 0.08% means there are about 0.08 grams of alcohol per deciliter of blood.

Our alcohol calculator uses information about your drinks, body weight, gender, and time since drinking began to estimate your current BAC. It also accounts for alcohol elimination over time.

Because alcohol absorption and metabolism vary from person to person, the result should always be treated as an estimate rather than an exact measurement.

How to Use the BAC Calculator

You can calculate your estimated blood alcohol level in a few steps:

1. Select your gender: Choose Male or Female from the dropdown.

2. Enter your body weight: Add your weight and select the appropriate weight unit.

3. Enter the time since your first drink: Provide the number of hours and minutes that have passed since you started drinking.

4. Add the alcohol consumed: Enter the amount of beer, wine, liquor, or another alcoholic drink you consumed.

5. Select the serving size and ABV: Choose the correct drink size and alcohol by volume (ABV). For a custom drink, enter its volume and ABV.

6. Click Calculate: The calculator estimates your BAC based on the information entered.

The calculator can also display estimated time to sober, pure alcohol consumed, alcohol weight in grams, and body weight used in the calculation. The available fields include separate entries for beer, wine, liquor, and other drinks.

How Is BAC Calculated?

The calculator uses a Widmark-based method to estimate blood alcohol concentration. This approach considers the amount of alcohol consumed, body weight, a body-water distribution factor, and the amount of time that has passed.

Widmark Formula

A commonly used version of the formula is:

$\mathrm{BAC} = \frac{W \times r \times A}{5.14} - (0.015 \times H)$

Where:

• BAC = estimated blood alcohol concentration

• A = alcohol consumed in fluid ounces

• W = body weight in pounds

• r = alcohol distribution ratio

• H = hours since drinking began

• 0.015 = assumed average BAC elimination per hour in this calculator

It currently uses this Widmark-based structure and an assumed elimination rate of approximately 0.015 BAC per hour.

The equation produces an estimate because the way alcohol is absorbed, distributed, and eliminated differs between people.

Calculating Pure Alcohol

Serving size alone does not tell you how much alcohol you consumed. The drink's ABV (alcohol by volume) also matters.

Pure alcohol can be estimated as:

$\text{Pure Alcohol Volume} = \text{Drink Volume} \times \frac{\text{ABV}}{100}$

For example, two drinks of the same size can contain very different amounts of alcohol when one has a higher ABV.

This is why the calculator asks for both serving size and alcohol percentage.

What Affects Your BAC?

Two people can consume the same number of drinks and have different BAC levels. Several factors influence how alcohol affects the body:

• Amount of alcohol: Consuming more pure alcohol generally increases BAC.

• Body weight: The same amount of alcohol can produce different estimated BAC levels at different body weights.

• Drink strength: Higher-ABV drinks contain more alcohol for the same serving volume.

• Serving size: A large pour may contain more than one standard drink.

• Drinking speed: Drinking several alcoholic beverages over a short period can cause BAC to rise quickly.

• Time: Your body begins eliminating alcohol over time.

• Food: Eating can affect how quickly alcohol is absorbed, but food does not remove alcohol already in your bloodstream.

• Individual differences: Body composition and alcohol metabolism vary from person to person.

A calculator cannot account perfectly for all of these differences.

BAC Levels and Possible Effects

Alcohol can affect judgment, coordination, reaction time, and other abilities. The exact effects at a particular BAC vary between individuals, so a BAC chart should be treated as general guidance rather than a prediction of how a specific person will feel.

Driving-related impairment can begin at BAC levels below 0.08 g/dL.

A person's apparent tolerance to alcohol does not mean important driving or decision-making abilities are unaffected.

BAC Calculator by Weight

A BAC calculator by weight considers body weight because alcohol is distributed through body water rather than remaining concentrated only in the alcohol consumed.

In general, the same amount of alcohol can produce a higher estimated BAC in a lower-weight person than in a higher-weight person when the other calculation variables are the same.

That does not mean a particular weight makes it safe to consume a certain amount of alcohol. Body composition, biological differences, drinking speed, food intake, and metabolism can all affect actual BAC.

What Is a Standard Drink?

A standard drink is based on the amount of pure alcohol, not simply the size of the glass, bottle, or can.

In the United States, one standard drink contains approximately 14 grams (0.6 fluid ounces) of pure alcohol.

Typical examples include:

These are only examples. A 12-ounce beer at 10% ABV, for instance, contains about twice as much pure alcohol as a 12-ounce beer at 5% ABV. NIAAA specifically notes that alcohol content can vary substantially even within the same type of beverage.

For the most accurate estimate possible, enter the actual serving size and ABV shown on the beverage.

How Long Does It Take for BAC to Go Down?

BAC generally decreases as the body metabolizes and eliminates alcohol. The blood alcohol level calculator uses an assumed average reduction of about 0.015 BAC per hour as part of its Widmark-based estimate.

Actual elimination rates vary, so the calculator's time to sober result is approximate.

Coffee, water, exercise, a cold shower, or sleep cannot instantly remove alcohol from your bloodstream. Feeling more awake also does not necessarily mean your BAC has returned to zero.

Time is necessary for the body to process alcohol.

BAC and Legal Driving Limits

There is no single BAC driving limit that applies everywhere in the world. Laws vary by country, state, driver age, license type, and other circumstances.

In most U.S. states, the per-se BAC limit for adult drivers is 0.08 g/dL; Utah uses 0.05 g/dL. Lower limits apply to certain drivers, including underage drivers.

However, a legal limit should not be interpreted as a safe-driving threshold. Driving ability can be impaired below 0.08 BAC.

If you have been drinking, do not rely on an online drunk calculator, estimated time-to-sober result, or how sober you feel to determine whether you can drive.

Limitations of a Blood Alcohol Calculator

A blood alcohol calculator cannot measure the actual concentration of alcohol in your blood. It can only estimate it from the information you provide and the assumptions built into its formula.

Actual BAC can differ because of factors such as:

• Individual alcohol metabolism

• Body composition

• Food intake and absorption

• How quickly drinks were consumed

• Incorrect serving-size estimates

• Incorrect ABV information

• Differences in alcohol distribution

• Timing of alcohol absorption and elimination

The calculation is especially sensitive to the amount of pure alcohol consumed, so accurately entering both drink size and ABV is important.

A BAC calculator does not replace a properly administered breath test, blood test, medical evaluation, or law-enforcement measurement.

Helpful Resources

• Alcohol and Public Health

• Alcohol Safety Information

• Understanding BAC

Pro Tips

• Drink responsibly and know your limits.

• Never drink and drive.

• Plan ahead for a safe way home if you plan to drink.

• Wait at least one hour per standard drink before driving.