Blood Alcohol Calculator
Estimate BAC using weight, drinks, alcohol percentage, and elapsed time.
A blood alcohol content calculator (also called a blood alcohol level calculator) estimates your approximate blood alcohol concentration based on the number of standard drinks consumed, your body weight, sex, and time elapsed since drinking began, using a version of the Widmark formula developed in the 1930s. This blood alcohol calculator over time is intended for general education about how alcohol affects the body - it is not a substitute for an actual bac test calculator device (breathalyzer or blood test) and should never be used to decide whether it's safe to drive.
Enter your weight, sex, number of standard drinks, and hours elapsed to see an estimated BAC level and how long it may take to return to zero.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| Male, 80 kg, 3 standard drinks, 2 hours elapsed | Estimated BAC ≈ 0.047% | 3 drinks ≈ 42g alcohol. BAC ≈ (42 ÷ (80,000g × 0.68)) × 100 − (0.015 × 2) ≈ 0.077% − 0.03% ≈ 0.047%. |
| Female, 65 kg, 3 standard drinks, 1 hour elapsed | Estimated BAC ≈ 0.102% | 3 drinks ≈ 42g alcohol. BAC ≈ (42 ÷ (65,000g × 0.55)) × 100 − (0.015 × 1) ≈ 0.117% − 0.015% ≈ 0.102% - notably higher than the male example with the same drink count, reflecting the lower body-water constant used for women in the Widmark formula. |
How the Widmark Formula Works
The Widmark formula estimates BAC using body water distribution, which differs by sex and body weight - it accounts for the fact that alcohol distributes through body water, and body water percentage varies between individuals, most notably averaging lower in women than men, which is one reason BAC estimates differ by sex for the same number of drinks and body weight. The formula then subtracts an estimated metabolism rate based on elapsed time, since the liver processes alcohol at a roughly constant rate over time.
Why This Is an Estimate, Not a Measurement
Actual BAC is affected by many factors this formula can't capture: how quickly you drank, whether you ate food beforehand, individual differences in liver function and metabolism, medication interactions, and the actual alcohol content of your specific drinks versus a standard drink assumption. A standard drink is typically defined as containing about 14 grams of pure alcohol - roughly a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits - but real drinks, especially mixed drinks and craft beers, often contain significantly more.
The Only Way to Actually Sober Up
The liver metabolizes alcohol at a roughly constant rate regardless of coffee, cold showers, or other common myths - time is the only thing that actually lowers BAC. Estimates of average metabolism rate are commonly cited around 0.015 BAC per hour, meaning a BAC of 0.08 would take roughly 5-6 hours to reach zero on average, though this varies by individual.
How to Use the Blood Alcohol Calculator
- Open the Blood Alcohol Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the blood alcohol calculator works.
Frequently Asked Questions
How accurate is a BAC calculator?
It provides a rough estimate only, based on averages for body weight, sex, and drink count. Actual BAC varies based on food intake, drinking speed, individual metabolism, and the real alcohol content of your drinks, so it should never be treated as a precise measurement.
What counts as one standard drink?
A standard drink is typically defined as containing about 14 grams of pure alcohol - roughly a 12 oz regular beer (5% ABV), a 5 oz glass of wine (12% ABV), or a 1.5 oz shot of spirits (40% ABV).
How long does it take for BAC to reach zero?
The liver metabolizes alcohol at a roughly constant average rate often cited around 0.015 BAC per hour, meaning a BAC of 0.08 takes roughly 5-6 hours on average to reach zero - though individual rates vary.
Does coffee or a cold shower lower BAC faster?
No. Neither affects how quickly the liver metabolizes alcohol. They may make someone feel more alert, but BAC itself only decreases with time.
Why does BAC differ between men and women for the same number of drinks?
The Widmark formula accounts for body water distribution, which on average differs by sex - this is one reason the same number of drinks and body weight can produce different estimated BAC levels between men and women.
Is it safe to drive if this calculator shows a low BAC?
No. This tool provides only a rough estimate and should never be used to judge whether it's safe to drive. If you've consumed any alcohol, arrange alternate transportation instead of driving.
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Last updated: September 27, 2026.