BAC Estimate Calculator
Estimate blood alcohol content (BAC) from actual drink volume, ABV, body weight, and elapsed time using the Widmark equation. Estimate only — not a breath or blood test, and not a driving-safety determination.
How It's Calculated
Formula
\text{BAC}(\%) = \max\left(0,\ \frac{A}{r \times W} \times 100 - 0.015 \times t\right)This calculator estimates blood alcohol content (BAC) using the Widmark equation, the standard model for relating consumed alcohol, body weight, and elapsed time to an estimated BAC. Alcohol consumed is calculated from actual serving volume and ABV (not a fixed "one drink" assumption): grams of ethanol = servings x volume per serving x ABV x ethanol density (0.789 g/mL). That mass is divided by body weight and a sex-based Widmark distribution factor (0.68 for men, 0.55 for women, reflecting average total-body-water differences), then reduced by a fixed elimination rate of 0.015% per hour. This is an estimate for general informational and educational purposes, based on a published formula — it is not a medical diagnosis, and it is not a substitute for individualized advice from a qualified healthcare provider. BAC varies substantially between individuals based on food intake, medication, metabolism, and other factors this formula cannot capture. This tool reports an estimated BAC percentage only — it is not a breath or blood test, and it must never be used to decide whether it is safe or legal to drive.
Worked Examples
Male, 70 kg, three 355 mL 5% beers, no elapsed time
- Ethanol grams: 3 x 355 mL x 0.05 x 0.789 = 42.01 g
- BAC = 42.01 / (0.68 x 70,000 g) x 100 - 0.015 x 0 ≈ 0.088%
Female, 60 kg, two 150 mL 12% wine glasses, 1 hour elapsed
- Ethanol grams: 2 x 150 mL x 0.12 x 0.789 = 28.40 g
- BAC = 28.40 / (0.55 x 60,000 g) x 100 - 0.015 x 1 ≈ 0.071%
Frequently Asked Questions
Can I use this to decide if it's safe or legal to drive?
No. This calculator reports an estimated BAC percentage only. It does not evaluate legal driving limits or driving safety in any jurisdiction, and it is not a breath or blood test. Do not use this estimate to decide whether to drive.
Why does biological sex affect the result?
The Widmark equation uses a sex-based distribution factor (0.68 for men, 0.55 for women) that reflects average differences in total body water, which affects how alcohol distributes through the body. It is used strictly as a formula input, not a lifestyle or identity classification.
Why isn't the elimination rate adjustable?
This calculator uses a fixed 0.015% per hour elimination rate, a commonly cited population average. Individual elimination rates typically range from about 0.010% to 0.020% per hour, so your actual BAC may differ from this estimate.
Why does this ask for serving volume instead of "number of drinks"?
"Drinks" has no fixed alcohol quantity — a can of beer, a glass of wine, and a shot of spirits contain very different amounts of alcohol. Entering the actual volume and ABV of what you drank produces a defensible ethanol-mass calculation instead of guessing a per-drink amount.