Blood Alcohol Content Calculator
Estimate your blood alcohol content from drinks, weight, sex, and time using the Widmark formula.
This calculator runs entirely in your browser. Nothing you enter is uploaded or stored.
Important: This BAC calculator gives a rough estimate for educational use only. It is not a medical or legal device and cannot tell you whether you are safe or legal to drive. Many factors it cannot see affect your real blood alcohol content. Never drive after drinking. When in doubt, do not drive.
How to use this tool
Enter how many standard drinks you have had, your body weight (and its unit), your sex, and the number of hours since your first drink. Then press Calculate BAC. The tool applies the Widmark formula to estimate your blood alcohol content as a percentage and shows roughly how long it would take for the alcohol to burn off. One standard US drink is about 14 grams of pure alcohol, which is one 12 oz beer at 5%, one 5 oz glass of wine at 12%, or one 1.5 oz shot of 80-proof spirits.
The Widmark formula
grams of alcohol = standard drinks x 14
r = 0.68 for males, 0.55 for females
The body weight is converted to grams, then multiplied by the distribution ratio r, which reflects how much of the body is water that alcohol spreads into. The body also clears alcohol at a steady rate of about 0.015% per hour, so that amount is subtracted for every hour since the first drink. If the result is below zero, it is shown as 0.00% because the alcohol has been processed.
A real example
Suppose a 160 lb male has 2 standard drinks and 1 hour has passed since his first drink. First, 160 lb converts to about 72,575 grams. The alcohol is 2 x 14 = 28 grams. So BAC = (28 / (72575 x 0.68)) x 100 - (0.015 x 1) = (28 / 49351) x 100 - 0.015 = 0.0567% - 0.015% = about 0.042%. After roughly 2.8 more hours of processing, that estimate would fall back to zero.
Common questions
How accurate is this BAC calculator?
It is only an estimate. The Widmark formula uses average values for body water and alcohol processing, but your real blood alcohol content depends on food in your stomach, hydration, medications, health, genetics, and how fast you drank. Treat the number as a rough guide, never as proof you are safe to drive.
What counts as one standard drink?
In the United States a standard drink contains about 14 grams of pure alcohol. That is roughly one 12 oz beer at 5% alcohol, one 5 oz glass of wine at 12%, or one 1.5 oz shot of 80-proof spirits. Large beers, cocktails, and craft brews often count as more than one drink.
How long does it take for alcohol to burn off?
The body clears alcohol at roughly 0.015% BAC per hour, and that rate does not change much. Coffee, cold showers, and water do not speed it up. The tool divides your estimated BAC by 0.015 to show the approximate hours until it returns to zero.
Why does sex change the result?
The formula uses a distribution ratio (r) of 0.68 for males and 0.55 for females. On average women have a higher proportion of body fat and less body water, so the same amount of alcohol spreads into a smaller volume and produces a higher BAC.
Can I rely on this to decide whether to drive?
No. This is an educational estimate, not a breathalyzer. Legal limits, your tolerance, and dozens of personal factors are not captured here. If you have been drinking, the only safe choice is to not drive. Use a rideshare, a taxi, or a sober driver.