Blood Alcohol Content Estimator

Estimate your blood alcohol concentration (BAC) based on drinks consumed, body weight, sex, and time elapsed.

Blood Alcohol Content Estimator tool

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Example

Input: Male, 80 kg, 3 standard drinks, 2 hours since first drink

Result: Estimated BAC 0.047 % (Mildly impaired), Total Alcohol Consumed 42 g, Time to Sober 3 hr 9 min

Widmark: 42 g / (80,000 g x 0.68) x 100 = 0.077%, minus 0.015% per hour x 2 hours = 0.047%.

Estimated BAC One Hour After the First Drink

Standard DrinksWoman, 60 kgMan, 80 kg
10.027%0.011%
20.070%0.036%
30.112%0.062%
40.155%0.088%
50.197%0.114%
60.240%0.139%

Widmark estimates only. Real BAC can be higher. Never use this table to decide whether to drive.

  1. Select your sex (male or female) for the correct Widmark body water ratio.
  2. Enter your body weight in kilograms.
  3. Enter the number of standard drinks consumed (14 grams of alcohol each; half drinks are allowed).
  4. Enter the hours elapsed since your first drink.
  5. View your estimated BAC, impairment status, total alcohol consumed, and time until sober.

How Blood Alcohol Content Is Estimated

Blood alcohol content (BAC) is the share of your blood that is alcohol. A BAC of 0.08% is the legal driving limit for adults in the US. This tool gives a rough estimate from your sex, weight, the number of standard drinks and the time since you started. It can never tell you if you are safe to drive.

It uses the Widmark formula. The grams of alcohol are divided by your body weight in grams times a body water factor: 0.68 for men and 0.55 for women. That figure is multiplied by 100. Then 0.015% is taken off for each hour since your first drink, the average rate at which the body clears alcohol. Each standard drink counts as 14 g of pure alcohol, the US definition.

For example, a man who weighs 80 kg and has 3 drinks has about 0.077% at the start. Two hours later that falls to an estimated 0.047%. The tool also gives an impairment status, the time until the estimate reaches zero and the total alcohol in grams. The table below shows how much the estimate changes with body size and sex. Alcohol also carries about 7 calories per gram, so those 3 drinks add roughly 290 calories. The Calorie Calculator shows how that fits into a day.

Real BAC can be much higher than the estimate. Drinking fast, drinking on an empty stomach, medicines, illness and differences in liver function all play a part. Drinks poured at home are often larger than a standard drink. Nothing speeds up how fast alcohol leaves your body: not coffee, water, cold showers or exercise.

Impairment starts well below the legal limit, and many countries set lower limits, such as 0.05%. Drivers under 21 and commercial drivers in the US face stricter limits. If you have been drinking, do not drive. Use a designated driver, a taxi or public transport. If someone has signs of alcohol poisoning, call emergency services.

Formula / How It Works

Widmark formula: BAC (%) = (alcohol in grams / (body weight in grams x r)) x 100 - (0.015 x hours). r = 0.68 for men, 0.55 for women. Standard drink = 14g pure alcohol.

Sources

Frequently Asked Questions

In the US, the limit is 0.08% for drivers aged 21 and over. Commercial drivers have a 0.04% limit, and drivers under 21 face near-zero limits. Many other countries use 0.05% or lower. Driving can be impaired below any legal limit, so the safest choice is not to drive after drinking.
In the US, one standard drink has about 14 g of pure alcohol. That is about 12 oz of regular beer at 5%, 5 oz of wine at 12%, or 1.5 oz of 40% spirits. Craft beers, large wine pours and mixed drinks often contain more than one standard drink.
On average, BAC falls by about 0.015% per hour, so a BAC of 0.08% takes over 5 hours to reach zero. This rate varies between people. Coffee, cold showers, water and exercise do not speed it up. Only time lowers BAC.
On average, women have less body water per kilogram than men, so the same alcohol is less diluted. The Widmark formula reflects this with a factor of 0.55 for women and 0.68 for men. Lower average body weight adds to the difference.
No. The formula uses averages and can underestimate your real BAC by a wide margin. Food, drinking speed, medicines and health all change the result. Only a breath or blood test measures BAC, and even a low reading does not mean you are unimpaired.

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