Alcohol Calculator (BAC)
Estimate Blood Alcohol Content — for educational use only
Enter total time from your first drink until now
What is it?
This calculator estimates Blood Alcohol Content (BAC) using the Widmark formula, based on your weight, gender, number of standard drinks, and time elapsed since your first drink.
Formula
BAC = (Alcohol grams ÷ (Weight × r × 1000)) × 100 − (0.015 × Hours)
r = 0.68 for men, 0.55 for women (body water ratio). One standard drink ≈ 14g of alcohol.
Formula Explanation
The Widmark formula estimates how much alcohol is distributed through your body water (approximated from body weight and a gender-based constant), then subtracts an average elimination rate of about 0.015% BAC per hour to account for alcohol your liver has already metabolized since you started drinking.
Example Calculation
A 70 kg man having 3 standard drinks over 2 hours has an estimated BAC of roughly 0.06% — in the "Mild" impairment range.
How to Use
- Enter your weight and select the unit.
- Select your gender.
- Enter the number of standard drinks consumed.
- Enter hours since your first drink.
- View your estimated BAC and impairment level.
Benefits
- Gives a rough, private way to understand alcohol's estimated effect on the body.
- Visualizes where an estimated BAC falls across recognized impairment ranges.
- Useful for general alcohol education and awareness.
Use Cases
- Understanding roughly how standard drinks and time affect estimated BAC.
- General alcohol safety education, such as understanding impairment stages.
- Illustrating why factors like weight and time change estimated BAC.
What Your Result Means
Your estimated BAC places you in a range from Minimal effects up to Severe impairment. This is a rough estimate only — actual BAC and impairment can be higher or lower than calculated depending on individual factors, and no BAC level is safe for driving.
Tips
- Never use this tool to decide whether it is safe to drive — always use a designated driver or alternate transport after drinking.
- Eating before and during drinking slows alcohol absorption, though it does not change the final calculated BAC.
- Pace drinks over time and stay hydrated with water between alcoholic drinks.
Common Mistakes
- Using this tool to judge fitness to drive — never drive after drinking, regardless of the estimated BAC.
- Underestimating drink size (a large glass of wine or strong cocktail may count as more than one standard drink).
- Ignoring that food, medication, and individual metabolism can significantly change actual BAC.
FAQs
How accurate is this BAC estimate?
The Widmark formula is a widely used approximation, but actual BAC varies with food intake, metabolism, medication, and individual physiology — never use this to decide if it's safe to drive.
What counts as one standard drink?
Roughly 14 grams of pure alcohol — about one 12 oz beer, one 5 oz glass of wine, or 1.5 oz of spirits.
Is it safe to drive at any calculated BAC?
No. This tool is for education only — never drive after drinking, regardless of the estimated BAC.
Why do men and women have different constants in the formula?
Women typically have a lower percentage of body water relative to weight than men, which affects how alcohol is diluted in the body, leading to generally higher BAC for the same amount consumed.
Does food affect BAC?
Eating slows the rate of alcohol absorption into the bloodstream, which can lower peak BAC and spread out its effects, though this calculator does not account for food intake.
How long does it take for BAC to return to zero?
The body eliminates alcohol at roughly 0.015% BAC per hour on average, so a BAC of 0.08% would take about 5-6 hours to fully clear, though individual rates vary.
Why does time since first drink matter?
Your body continuously metabolizes alcohol, so the formula subtracts an estimated elimination amount based on how long you've been drinking to reflect that ongoing process.
Can two people with the same inputs have different actual BAC?
Yes — individual factors like metabolism, medication use, and overall health can cause real BAC to differ from this formula's estimate, even with identical inputs.
References
This tool is for educational purposes only. BAC varies by metabolism, food, and health conditions.
Last updated: July 25, 2026