Blood Alcohol (BAC) Calculator
Estimate your blood alcohol content (BAC) from the number of standard drinks, body weight, sex and time elapsed, using the Widmark formula. For education only. Private.
Last reviewed by the Radiatus Cloud team
Need this done properly for your business?
Radiatus delivers secure cloud, DevOps & compliance engineering.
Estimate blood alcohol from drinks and body weight
Blood Alcohol Content estimates the concentration of alcohol in your bloodstream. This calculator estimates it from the number of standard drinks, your body weight, sex and the time elapsed, giving a rough sense of impairment, though it is an estimate only and must never be treated as a licence to drive.
Why any BAC estimate is only approximate
BAC depends on far more than a formula can capture: what and when you last ate, your hydration, your liver’s rate of processing, medications, and individual physiology all shift the real value. The calculation gives a population-average estimate, and your actual BAC could be meaningfully higher. The body clears alcohol at a roughly fixed rate over time, which is why the elapsed time reduces the estimate, but that rate too varies between people.
A safety message, not a green light
The only safe amount of alcohol before driving is none, and no calculator can tell you that you are under a legal limit reliably enough to risk it. Treat any estimate as a reason to be cautious, never as permission. This is general information, not medical or legal advice. The calculation runs in your browser, so your input is not uploaded.
Related tools
- Percentage Calculator — Calculate percentages, percentage change, increase and decrease, and reverse percentages, with the working shown for each result.
- Statistical Calculator — Calculate mean, median, mode, standard deviation, and more.
- Probability Calculator — Calculate probabilities for single and combined events, including conditional probability and Bayes' theorem.
- Scientific Calculator — Perform advanced mathematical operations including trig, log, and exponents.
Frequently Asked Questions
How is BAC estimated?
From the number of standard drinks, your body weight and sex, and the time elapsed, using a population-average formula. Your actual value can differ significantly.
Can I use this to decide whether to drive?
No. The only safe amount before driving is none. No calculator is reliable enough to risk driving on, because real BAC depends on many factors a formula cannot capture.
Why does time reduce the estimate?
Because the body clears alcohol at a roughly fixed rate, so more elapsed time means a lower estimate. That rate varies between people, adding to the uncertainty.
What affects real BAC beyond the inputs?
Food, hydration, liver function, medications and individual physiology all shift it, which is why the estimate is approximate and can understate your true level.
Is this medical or legal advice?
No. It is general information only. Never treat it as permission to drive.
Privacy & Security
All processing happens locally in your browser — nothing is uploaded.
How to Use
Enter drinks, weight, sex and hours since your first drink. This is an estimate — never drink and drive.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
Percentage Calculator
MathCalculate percentages, percentage change, increase and decrease, and reverse percentages, with the working shown for each result.
Statistical Calculator
MathCalculate mean, median, mode, standard deviation, and more.
Probability Calculator
MathCalculate probabilities for single and combined events, including conditional probability and Bayes' theorem.