BAC Calculator
A rough estimation of Blood Alcohol Content (BAC) based on weight, gender, drinks consumed, and time elapsed.
Complete Guide: BAC Calculator
Everything you need to know about using this tool effectively
Enter your weight, gender, number of standard drinks consumed, and hours since your first drink to estimate your blood alcohol content (BAC). The calculator uses the Widmark formula and shows your BAC percentage, estimated time until sober, and whether you are above common legal driving limits. This tool is for educational purposes only.
The Widmark formula calculates BAC as (A / (r * W)) - 0.015 * H, where A is alcohol consumed in grams, r is the body water ratio (0.68 for males, 0.55 for females), W is body weight in grams, and 0.015 is the average alcohol elimination rate per hour, and H is hours elapsed. One standard drink contains approximately 14 grams of alcohol.
Responsible drinking awareness
Understand how alcohol affects your body over time and when you might be safe to drive.
Party planning
Estimate how different amounts of alcohol will affect guests of varying weights and genders.
Educational purposes
Learn how the Widmark formula works and how BAC is calculated in pharmacology.
Personal tracking
Track your consumption during a night out to make more informed decisions about transportation.
Enter your body weight and gender
These values determine the body water ratio used in the Widmark formula.
Input number of drinks and time elapsed
Enter how many standard drinks you have had and how many hours since your first drink.
Review your estimated BAC
The calculator shows your current BAC, legal limit status, and estimated time until sober.
A standard drink is 12 oz of beer, 5 oz of wine, or 1.5 oz of spirits
Food in your stomach slows absorption but this calculator uses average elimination rates
Never use this calculator as a substitute for a breathalyzer or professional judgment
The elimination rate of 0.015 percent per hour is an average and varies between individuals
What is the Widmark formula?
The Widmark formula estimates BAC by dividing the grams of alcohol consumed by the product of body weight and a gender-specific body water ratio, then subtracting the elimination over time. It was developed by Swedish scientist Erik Widmark in the 1930s.
Why does gender affect the calculation?
On average, males have a higher proportion of body water (r = 0.68) compared to females (r = 0.55). This means the same amount of alcohol produces a higher BAC in females, all else being equal.
How accurate is this BAC estimate?
The Widmark formula provides a reasonable estimate but individual factors like metabolism, food intake, medications, and tolerance can cause actual BAC to vary by 10 to 20 percent from the calculated value.
Can I rely on this to decide if I can drive?
No, this calculator is for educational purposes only. Never rely on an estimate to make driving decisions. Use a certified breathalyzer or arrange alternative transportation if you have been drinking.
What counts as a standard drink?
In the United States, a standard drink contains about 14 grams of pure alcohol. This equals 12 ounces of 5 percent beer, 5 ounces of 12 percent wine, or 1.5 ounces of 40 percent distilled spirits.