BAC Calculator
Estimate blood alcohol concentration based on relevant inputs.
Understanding BAC Calculator
Blood Alcohol Concentration (BAC) describes the amount of alcohol present in the bloodstream and is commonly expressed as a percentage. BAC changes over time as alcohol is absorbed into the bloodstream, distributed throughout the body's water-containing tissues, and gradually eliminated. The amount consumed is an important factor, but BAC is also influenced by body weight, body composition, biological sex, drinking speed, food intake, and individual differences in alcohol absorption and metabolism.
This BAC calculator provides a mathematical estimate using a simplified Widmark-style calculation. It uses the entered body weight, sex, number of standard drinks, and elapsed time to estimate an initial BAC and then applies an assumed alcohol elimination rate. Because the calculation relies on population-level assumptions, the result should not be considered a measurement of an individual's actual blood alcohol concentration.
A practical way to use this calculator
To use BAC Calculator effectively, enter the values requested by the calculator and keep their units and meaning consistent. The main information requested on this page includes Gender, Weight (kg), Number of Standard Drinks, Hours Since Drinking Began. If the calculator offers selectable methods or options, choose the one that matches the question you are trying to answer.
What this calculation can and cannot tell you
The result is calculated from the inputs shown on this page, so it is most useful when you understand what each input represents. Before relying on the number, check the units, the scale of the result, and any assumptions described above the calculator.
About BAC Calculator
Blood Alcohol Concentration (BAC) describes the amount of alcohol present in the bloodstream and is commonly expressed as a percentage. BAC changes over time as alcohol is absorbed into the bloodstream, distributed throughout the body's water-containing tissues, and gradually eliminated. The amount consumed is an important factor, but BAC is also influenced by body weight, body composition, biological sex, drinking speed, food intake, and individual differences in alcohol absorption and metabolism.
This BAC calculator provides a mathematical estimate using a simplified Widmark-style calculation. It uses the entered body weight, sex, number of standard drinks, and elapsed time to estimate an initial BAC and then applies an assumed alcohol elimination rate. Because the calculation relies on population-level assumptions, the result should not be considered a measurement of an individual's actual blood alcohol concentration.
The calculator assumes that one standard drink contains approximately 14 grams of pure alcohol. The actual amount of alcohol in a beverage depends on its volume and alcohol-by-volume percentage. A large beer, glass of wine, cocktail, or other alcoholic beverage may therefore contain more or less alcohol than one standard drink depending on its size and strength. Definitions of a standard drink also vary between countries.
How the BAC Calculation Works
The calculation first estimates the total amount of pure alcohol consumed from the number of standard drinks entered. It then relates that alcohol amount to body weight and an estimated body-water distribution factor. Finally, an assumed elimination rate is subtracted according to the number of hours entered.
Alcohol = Standard Drinks × 14 g
Estimated Initial BAC
BAC ≈ [Alcohol (g) ÷ (Weight (kg) × Distribution Factor × 1000)] × 100
Estimated BAC After Time
BAC ≈ Initial BAC − (0.015 × Hours)
Factors That Can Affect BAC
Actual BAC can differ from a calculator estimate for many reasons. Alcohol may be absorbed at different rates depending on whether a person has eaten, how quickly the drinks were consumed, and the concentration of alcohol in the beverages. Body composition can also influence alcohol distribution. Liver function, medications, illness, drinking pattern, and individual metabolic differences can affect how alcohol is processed and eliminated.
The timing of drinking is particularly important. Consuming the same total amount of alcohol over a short period can produce a different BAC pattern from consuming it gradually over several hours. The calculator cannot reproduce all of these physiological processes, so its output should be treated only as an approximate mathematical estimate.
Understanding the Result
The result section provides more than the estimated BAC number. It shows the entered body weight, number of standard drinks, elapsed time, estimated amount of pure alcohol consumed, distribution factor, estimated BAC before elimination, estimated elimination, and the resulting estimated BAC. These details explain how the displayed value was obtained.
Weight: 70 kg
Standard Drinks: 2
Time Since Drinking Began: 2 hours
Sex: Male
Estimated Alcohol Consumed:
2 × 14 = 28 g
Distribution Factor:
0.68
Estimated Elimination:
0.015 × 2 = 0.030 percentage points
The final estimated BAC is obtained by subtracting the assumed elimination from the estimated initial BAC.
Standard Drinks and Alcohol Content
A standard drink is intended to represent a specific quantity of pure alcohol, but the definition is not identical worldwide. The alcohol content of an actual beverage depends on both serving size and alcohol concentration. For this reason, simply counting glasses, cans, or bottles does not always provide an accurate estimate of the number of standard drinks consumed.
Why BAC Estimates Are Limited
A mathematical BAC estimate cannot account for every factor involved in alcohol absorption and elimination. It does not directly measure blood alcohol concentration, and the assumed elimination rate is not guaranteed to match an individual's physiology. Consequently, even a carefully calculated result may differ significantly from a value obtained through an appropriate alcohol-testing method.
BAC should also not be confused with how intoxicated a person feels. Alcohol tolerance can change subjective feelings without preventing alcohol from affecting reaction time, coordination, attention, judgment, and decision-making. A person may therefore be impaired even when they feel relatively normal.
This calculator provides an estimate only. It cannot confirm sobriety, determine actual BAC, or establish whether driving is safe or legally permitted.
Driving and Safety
Do not use a calculated BAC value to decide whether to drive, operate machinery, swim, work at heights, or perform another potentially dangerous activity. Legal BAC limits vary by jurisdiction and may also depend on the type of driver or vehicle. If alcohol has been consumed, the safest choice is to avoid driving and use a sober driver, taxi, public transportation, rideshare service, or another safe alternative.
Medical Disclaimer
This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for medical decisions.