BAC Estimates: How the Widmark Formula Works
The Widmark formula turns drinks, weight, and time into a rough blood alcohol figure. This post explains each input and why the result stays an estimate.
What is the BAC Estimator?
This estimator uses the Widmark formula as a rough guide: it spreads the alcohol across body water by sex, then subtracts a steady elimination rate over time. It is an estimate only and never a reason to drive — the only safe choice after drinking is not to drive. This tool is not medical advice; if you feel unwell after drinking, seek help.
How to use it
- Enter how many standard drinks you had.
- Enter your body weight and select the formula set.
- Enter the hours since your first drink.
- Click Estimate BAC.
Worked example
3 standard drinks for a 75 kg man after 2 hours gives an estimated BAC of about 0.05 percent.
Can a BAC estimate say I am safe to drive?
No. Estimates vary too much to clear anyone to drive, and legal limits differ by place. After drinking, do not drive.
Frequently asked questions
What is a standard drink here?
One standard drink is counted as 14 g of pure alcohol, the US convention used by this formula.
Why does sex change the result?
The formula uses a different body-water factor for men and women, which changes how the same alcohol spreads.