Do not use this result to drive: A formula cannot measure your BAC or determine impairment, safety, fitness to drive, or legal status. If you have been drinking, do not drive. Arrange a sober driver, taxi, or rideshare.
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How to Calculate Blood Alcohol Content: Widmark Formula and Worked Example
The standard method for calculating blood alcohol content is the Widmark formula, used in toxicology and forensic science since 1932. It estimates BAC from body weight, gender, total alcohol consumed, and time elapsed since drinking began.
BAC = (oz_alcohol x 5.14 / body_weight_lbs / r) - (0.015 x hours) r = 0.73 (male), 0.66 (female), Widmark distribution factor 1 standard drink = 0.6 oz pure alcohol
The 5.14 constant converts fluid ounces of alcohol to grams and adjusts units. The r factor (Widmark factor) represents the fraction of body weight that is water, which varies by gender. The 0.015 subtraction accounts for the liver eliminating approximately 0.015% BAC per hour.
Worked example: A 160 lb male drinks 3 regular beers (0.6 oz alcohol each) starting at 8 pm. It is now 9 pm, 1 hour elapsed.
Total alcohol: 3 x 0.6 oz= 1.8 oz
Numerator: 1.8 x 5.14= 9.252
Denominator: 160 x 0.73 (male r)= 116.8
Before elimination: 9.252 / 116.8= 0.0792%
Elimination: 0.015 x 1 hour= -0.015%
Estimated BAC0.064% model output
The 0.064% figure is only the formula output for the example inputs. It cannot establish the person's actual BAC, degree of impairment, ability to drive, or legal status. Alcohol metabolism intersects with blood glucose regulation; the A1C Calculator provides context on long-term glucose control, which regular alcohol consumption affects.
Why a BAC Estimate Is Not a Safety Threshold
This formula cannot observe alcohol absorption, body composition, genetics, liver function, medication interactions, actual pour sizes, or whether drinking continued after the entered time. Those unknowns can make the displayed estimate differ from a breath or blood measurement.
It cannot measure current BAC
It cannot determine degree of impairment
It cannot determine fitness to drive
It cannot determine legal status in any jurisdiction
Alcohol Metabolism Is Not a Countdown
The subtraction used by the model is a population-level assumption. The National Institute on Alcohol Abuse and Alcoholism notes that metabolism varies widely among individuals. A calculator therefore cannot predict when a specific person will reach a particular measured BAC or become safe to drive.
Possible alcohol overdose is an emergency. Call local emergency services for confusion, inability to wake, vomiting, seizures, slow or irregular breathing, clammy or bluish skin, or very low body temperature. Do not wait for a calculator result or assume the person can sleep it off.
What Blood Alcohol Content Depends On: Weight, Gender, and Food
Five variables determine blood alcohol content: total alcohol consumed, body weight, gender, time elapsed, and whether you ate before drinking. Body weight and gender have the largest individual-to-individual impact on BAC for the same number of drinks.
Profile
Weight
Drinks
Hours
Estimated BAC
Male (r = 0.73)
140 lbs
3 regular beers
1 hr
0.076% model output
Female (r = 0.66)
140 lbs
3 regular beers
1 hr
0.085% model output
The two model outputs differ because the selected Widmark distribution factors differ. These factors are population averages; they cannot represent an individual's actual body composition, absorption, or metabolism. The Army Body Fat Calculator also uses body weight and gender in its Hodgdon-Beckett circumference formula.
Food can affect the rate of alcohol absorption, but eating does not make a formula result a measurement or make driving safe. This simplified calculator does not model meal timing, stomach contents, or individual absorption.
Common BAC Calculation Mistakes
Treating a serving as a verified standard drink
Container size, pour size, and alcohol percentage vary. If an input is wrong, the formula output will also be wrong.
Assuming food or coffee removes impairment
Food can affect absorption, while coffee may change how alert someone feels. Neither turns a calculator estimate into proof of sobriety or fitness to drive.
Using any displayed number to justify driving
The model cannot measure current BAC or establish impairment, safety, fitness to drive, or legal status. Never use its output for a driving decision.
Treating elapsed time as a countdown
The formula uses a fixed subtraction for elapsed time, but real metabolism varies widely. It cannot predict when a specific person will reach a measured BAC or be safe to drive.
Ignoring medicines and health conditions
Medicines, health conditions, genetics, and individual physiology can affect alcohol response and are not captured by this simplified model.
HR
Hassaan Rasheed
Developer and Researcher, CalculatorFlux
Researches and verifies the formulas, methodology, and source data behind each calculator on CalculatorFlux. All tools are built and checked against the cited references before publication.
Widmark EMP: Principles and Applications of Medicolegal Alcohol Determination (1981)
Frequently Asked Questions
It applies a simplified Widmark formula to the entered body weight, distribution-factor selection, alcohol amount, and elapsed time. It is a mathematical estimate, not a breath or blood measurement.