BAC Calculator
Enter your weight, sex, the number of standard drinks and the hours since you started. We estimate your blood alcohol content and how long it takes to clear.
This calculator gives general estimates for information only. It is not medical advice and does not replace a consultation with a doctor or other qualified health professional.
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The formula
BAC % = alcohol (g) / (body weight (g) x r) x 100 - 0.015 x hours. r = 0.68 for men and 0.55 for women (Widmark).
Please read this first
This is a rough estimate. Real blood alcohol depends on food, medication, health, how fast you drank and your own body. Impairment starts well below any legal limit, and you should never drive after drinking. If in doubt, do not drive.
What counts as a drink
In this calculator one standard drink contains 14 grams of pure alcohol. That is roughly a 355 ml (12 oz) beer at 5 percent, a 148 ml (5 oz) glass of wine at 12 percent, or a 44 ml (1.5 oz) shot of spirits at 40 percent. Pour sizes in many bars and homes are bigger than this.
How the estimate works
The Widmark formula divides the alcohol you drank by your body weight and how much of your body is water, because alcohol spreads through body water. Women on average have a lower proportion of body water, which is why the factor is lower, and BAC rises higher for the same drinks and weight.
The body clears roughly 0.015 percent BAC per hour, so we subtract that for the time that has passed. It takes about 4 to 5 hours to clear after four or five drinks.
Legal limits differ
Limits vary by country: for example 0.08 percent in most of the US, 0.05 percent in many European countries and Australia, and lower again for new or professional drivers. Check your local rules, and treat them as a ceiling, not a safe level.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Male; Weight (lb): 180; Standard drinks (14 g alcohol each): 4; Hours since the first drink: 2 | Estimated BAC now: 0.071% |
| Female; Weight (kg): 60; Standard drinks (14 g alcohol each): 3; Hours since the first drink: 1 | Estimated BAC now: 0.112% |
| Male; Weight (kg): 90; Standard drinks (14 g alcohol each): 2 | Estimated BAC now: 0.046% |
BAC Calculator: frequently asked questions
Can coffee or a cold shower sober me up?
No. Only time reduces blood alcohol.
Is this good enough to decide whether I can drive?
No. Never use an estimate to decide whether it is safe to drive.
Can I rely on this result as medical advice?
No. It is a general estimate for information only. It cannot replace a check-up, and your doctor can interpret the numbers for your own situation.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026