The formula
How it works
Blood alcohol concentration (BAC) estimates how much alcohol is in your bloodstream. This calculator uses the Widmark formula from your weight, sex, number of drinks and time. It is an estimate only — never use it to decide whether to drive.
FAQ
What is a “standard drink”?
About 14 grams of pure alcohol — roughly a 12 oz beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits. Many real drinks contain more than one standard drink.
How accurate is this?
It is a rough estimate. Real BAC depends on food, hydration, medication, health and how fast you drank. Never rely on any calculator to judge if you are safe or legal to drive.
Does eating food lower my BAC?
Food does not lower the total amount of alcohol you absorb, but it slows absorption so your BAC rises more gradually and peaks lower than drinking on an empty stomach. This calculator assumes steady absorption and does not adjust for food.
Why does the calculator use different ratios for men and women?
The distribution ratio approximates how much of the body is water, which dilutes alcohol, and women on average have a higher proportion of body fat to water than men. That is why the same drinks and weight produce a higher estimated BAC for women in the Widmark formula.
Does coffee or a cold shower sober you up faster?
No — only time lowers BAC, since the liver metabolizes alcohol at a fairly fixed rate regardless of caffeine or cold water. Coffee can make you feel more alert while your BAC is unchanged, which is part of why it is dangerous.
How long until I reach zero?
The calculator divides your estimated BAC by the average elimination rate of about 0.015% per hour to give a rough time to zero, shown in the breakdown. This is only an average; individual metabolism varies.
Are legal driving limits the same everywhere?
No — many places use 0.08% for general drivers, but some countries and many jurisdictions set lower limits, such as 0.05% or 0.02%, and often a much lower or zero limit for commercial and novice drivers. Always check the specific limit where you are.
About the BAC calculator
This calculator estimates blood alcohol concentration — the percentage of alcohol in your blood — from your body weight, sex, how many drinks you have had and how long ago you started. BAC is what breathalysers and blood tests measure, and it is the number the law uses to define drink-driving limits. This tool is for education and curiosity only; it can never tell you it is safe or legal to drive.
How to use it
Choose your sex and weight units, then enter your body weight, the number of standard drinks you have had, and the hours since your first drink. The calculator returns an estimated BAC as a percentage. For example, a 80 kg man who has had three standard drinks over one hour comes out around 0.06%. Because your body clears alcohol steadily over time, the estimate falls the longer it has been since you started drinking.
The formula
This uses the Widmark equation, , where is the grams of pure alcohol, is body weight in grams and is a distribution ratio — about 0.68 for men and 0.55 for women, reflecting differences in body water. Each standard drink adds roughly 14 grams of alcohol. The final term subtracts elimination over time, with about 0.015% per hour as the body metabolises alcohol.
Where it is used
The Widmark formula is the standard used in forensic science and toxicology to estimate BAC, including in legal cases where a reading must be worked back to the time of driving. Educators and health campaigns use calculators like this to show how quickly a few drinks add up, and how long alcohol lingers. It is a teaching tool for responsible drinking — not a substitute for a breathalyser or plain common sense.