Estimate your blood alcohol concentration (BAC) with the Widmark formula based on sex, weight, number of standard drinks, and time elapsed.
Estimated BAC
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-Educational estimate only. The Widmark formula is an approximation and ignores food, drinking pace, medications, and individual differences. It cannot tell you whether you are safe or legal to drive. Never drink and drive.
Example
An 80 kg man drinks 3 standard drinks (3 × 14 g = 42 g of alcohol) over 2 hours:
peak BAC = (42 / (80000 g × 0.68)) × 100 = 0.0772%
metabolized = 0.015 × 2 hr = 0.030%
estimated BAC = 0.0772% - 0.030% = 0.047%
Result: about 0.047% BAC - below the US 0.08% legal limit, but still impaired.
How it works
Enter alcohol consumed as standard drinks (each ~14 g pure alcohol), your weight, sex, and hours since your first drink. The tool applies the Widmark equation, subtracting 0.015%/hour for metabolism.
Good to know
The BAC Calculator estimates your blood alcohol concentration using the Widmark equation, the same formula taught in forensic toxicology. You enter your sex, body weight (in kilograms or pounds), the number of US standard drinks you've had (each counted as about 14 grams of pure alcohol), and how many hours have passed since your first drink. It then returns an estimated BAC percentage, the total grams of alcohol consumed, how much your body has already metabolized, and a rough "time to sober" countdown. It's aimed at anyone curious about how alcohol math works, not at making real-world decisions about driving.
People typically reach for a tool like this to understand the mechanics behind a number they've seen on a breathalyzer, to compare how the same drinks affect different body weights, or to see why sex changes the result. The calculator builds in the standard assumptions: a metabolism rate of 0.015% per hour and Widmark "r" factors of 0.68 for men and 0.55 for women, which reflect differences in average body-water percentage.
Read the output alongside the color-coded badge, which sorts the estimate into bands from "minimal impairment" up to "dangerous." Remember the result is a single estimate, not a range, and the "metabolized" figure is simply 0.015 multiplied by the hours you entered, so a fresh drink that hasn't absorbed yet can make a real breath test read higher than this number suggests.
One practical caveat: the formula assumes all the alcohol is already in your bloodstream and ignores food, drinking pace, hydration, medications, and individual liver differences, so treat any value near a legal threshold as meaningless for deciding whether to drive. The only reliable BAC is one measured by an actual breath or blood test, and the safest BAC behind the wheel is zero.
Frequently asked questions
What counts as one standard drink?
A US standard drink contains about 14 grams of pure alcohol - roughly a 12 oz beer (5%), a 5 oz glass of wine (12%), or a 1.5 oz shot of 80-proof spirits (40%). This tool multiplies your drink count by 14 g.
Why are the male and female r values different?
The Widmark factor r reflects the fraction of body mass that is body water, which distributes alcohol. Men average about 0.68 and women about 0.55 because women typically have a higher body-fat percentage, so the same dose yields a higher BAC.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
How accurate is the Widmark BAC formula?
The Widmark equation gives a population-level approximation that can differ substantially from a measured BAC for any individual. It does not account for food in the stomach, drinking speed, absorption time, medications, age, or genetic variation in alcohol metabolism, so it should be treated as educational rather than precise.
Does drinking water or coffee lower your BAC?
No. Only time allows the liver to metabolize alcohol, at a roughly fixed rate. Water, coffee, food, or a cold shower may make you feel more alert but do not speed up the elimination of alcohol from your blood.
How long does it take for BAC to return to zero?
Because the body eliminates alcohol at about 0.015% per hour, a BAC of 0.08% takes roughly five to six hours to reach zero. This calculator's 'time to sober' field divides your estimated BAC by 0.015 to show an approximate figure.
Why does the same number of drinks give women a higher BAC than men?
Women on average have a lower proportion of body water relative to body mass, so alcohol is distributed in a smaller volume and reaches a higher concentration. The formula captures this with a lower distribution factor for women than for men.
Can this calculator tell me if I'm legal to drive?
No. It produces an estimate that cannot reflect your actual blood alcohol level at a given moment, and impairment can occur below any legal limit. It should never be used to decide whether to drive.
Does body weight affect how drunk you get?
Generally, a heavier person has more body water to dilute the same amount of alcohol, producing a lower BAC than a lighter person who drank the same amount. Body composition matters too, since fat tissue holds little water.
How many drinks does it take to reach 0.08%?
It varies widely with weight, sex, and time, so there is no fixed number. For a smaller person a couple of standard drinks in a short period can approach that level, while a larger person may need more, but only a measured test can confirm an actual BAC.
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