BAC CalculatorFree online fitness & health calculator — instant results, no sign-up
Estimated blood alcohol content (Widmark). Never drink and drive.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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About the BAC Calculator
This calculator estimates Blood Alcohol Content (BAC) percentage and the time required for alcohol to clear from the bloodstream. It uses the Widmark formula to model alcohol distribution and average metabolic breakdown based on biological sex, body weight, standard drinks consumed, and elapsed time.
- Sex
- Biological sex (Male or Female), used to select the body water distribution ratio (0.68 for males, 0.55 for females).
- Weight
- Total body weight in kilograms (kg), typically between 40 kg and 200 kg.
- Standard drinks
- Number of standard alcoholic drinks consumed, defined as containing 14 grams of pure alcohol each.
- Hours since first drink
- Total elapsed time in hours from the start of drinking to the current moment.
Formula and method
BAC = max(0, ((Drinks × 14) / (Weight × 1000 × r)) × 100 − (0.015 × Hours)) Hours until ~0 = BAC / 0.015
- BACEstimated Blood Alcohol Content as a percentage (g/100 mL)
- DrinksNumber of standard drinks (14 grams of alcohol each)
- WeightBody weight in kilograms
- rGender-specific Widmark distribution factor (0.68 for males, 0.55 for females)
- HoursElapsed time since the first drink began
- 0.015Average rate of alcohol metabolism per hour (% BAC reduction)
The tool calculates total alcohol consumed in grams (drinks multiplied by 14) and divides it by the total body water weight (body mass in grams multiplied by factor r), converting it to a percentage. It then subtracts a steady metabolic reduction of 0.015% per hour, clamping negative values to zero. The remaining BAC is divided by 0.015 to estimate the hours needed to reach zero.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- SexMale
- Weight75 kg
- Standard drinks3
- Hours since first drink2
Results
- Estimated BAC0.052%
- Hours until ~03.5
- NoteEstimate only — never drive after drinking
How to use the BAC Calculator
- 1Multiply the number of standard drinks by 14 to determine total alcohol intake in grams.
- 2Convert body weight to grams and multiply by the gender factor (0.68 for male, 0.55 for female) to estimate effective body water mass.
- 3Divide alcohol grams by body water grams, multiply by 100 to get peak BAC percentage, and subtract 0.015 multiplied by elapsed hours.
- 4Ensure the BAC does not drop below 0%, round the final BAC to 3 decimal places, and divide it by 0.015 to calculate hours until sober.
Reading your result
The primary result shows your estimated current BAC as a percentage. The 'Hours until ~0' indicates approximately how long your body will take from the current moment to metabolize remaining alcohol. Because individual metabolic rates vary significantly, this estimate should never be used to decide fitness to drive.
Limitations
The calculation relies on average constants and assumes a fixed elimination rate of 0.015% per hour. It does not account for food consumption, stomach contents, medications, liver health, hydration, or variations in individual metabolic rates.
Common questions
What constitutes one standard drink in this calculator?+
The model uses the standard United States definition of one standard drink, which corresponds to 14 grams (about 0.6 fluid ounces) of pure ethanol, typically found in 12 oz of regular beer, 5 oz of wine, or 1.5 oz of 80-proof spirits.
Why does biological sex affect the calculated BAC?+
On average, women have a lower percentage of body water and higher body fat ratio than men of the same weight. The Widmark factor accounts for this difference in distribution volume (0.55 for females versus 0.68 for males).
Can drinking water or coffee speed up the time to reach zero BAC?+
No. The liver metabolizes alcohol at a relatively constant biological rate (modeled here at 0.015% per hour). Water prevents dehydration and coffee increases alertness, but neither speeds up ethanol elimination from the bloodstream.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.