Blood Alcohol Calculator — A Rough Widmark Estimate of BAC

How to use the blood alcohol calculator

1. Enter the Number of drinks and the Volume per drink in ml.
2. Enter the Alcohol strength in % ABV, from the label.
3. Enter your Body weight in kg and choose your Sex.
4. Enter the Hours since the first drink.
5. Read the estimated BAC, the same figure in g/L, the grams of alcohol you drank and a rough time until it reaches zero. Read the warning above the result first.

What it does and when to use it

The calculator shows how blood alcohol builds up and falls over time, using the classic Widmark formula. It can help you understand why a few drinks take hours to clear, or how drink size and strength add up. It cannot tell you whether you are safe or legal to drive, and it shows no legal limits. For other health estimates, see the BMI Calculator, the Blood Pressure Calculator and the Sleep Calculator.

How it works

• Alcohol (g) = drinks × volume (ml) × ABV ÷ 100 × 0.789 (the density of ethanol, g/mL)
• Peak BAC (%) = alcohol (g) ÷ (body weight in g × r) × 100
• Estimated BAC now = peak BAC − 0.015 × hours, never below zero
• Time until zero = estimated BAC ÷ 0.015

The elimination rate of 0.015% per hour is the population average for moderate drinkers in Jones’s 2010 review; the real range is about 0.010% to 0.035% per hour. The factor r is the share of body weight that alcohol spreads into: 0.68 for men and 0.55 for women in this calculator. These are conventional averages attributed to Widmark’s original work, which is not available online, so we have not confirmed them from a primary source. Forensic researchers such as Maskell and colleagues (2020) prefer estimates based on total body water from height, weight, age and sex, which this calculator does not use. That is why this page is held back from search results for now.

Worked examples

Three 330 ml beers at 5%, a 75 kg man, 2 hours after the first. That is 39.1 g of alcohol: Estimated BAC: 0.047%, with roughly 3.1 hours until zero.

Two 150 ml glasses of 12% wine, a 60 kg woman, 1 hour after the first. That is 28.4 g of alcohol: Estimated BAC: 0.071%, with roughly 4.7 hours until zero.

Limits and tips

• It assumes all the alcohol is absorbed at once. In reality it takes time, faster on an empty stomach and slower after food, so BAC can still be rising after you stop.
• Fixed body-water factors. Your own value may be well above or below 0.68 or 0.55.
• Average elimination. Some people clear alcohol much more slowly or quickly than 0.015% per hour.
• No legal advice. Drink-driving limits differ by country and by type of driver. Do not use this tool to judge whether you are under any limit.