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This calculator gives a rough estimate of blood alcohol content (BAC) using the Widmark formula, based on how many standard drinks you’ve had, your body weight and sex, and how long ago you started.
It is an estimate only, and it must never be used to decide whether it is safe or legal to drive. Real BAC varies with food, drink strength, medication, health and individual metabolism in ways no formula can capture. If you have been drinking, do not drive.
How is it calculated?
The Widmark formula
BAC is estimated as the alcohol in your body divided by the water your body can distribute it through, minus what your liver has already cleared:
BAC% = (drinks × 14 g ÷ (weight in grams × r)) × 100 − 0.015 × hours
| Factor | Value |
|---|---|
| Standard drink | 14 g of pure alcohol |
| r (distribution) | 0.68 male, 0.55 female |
| Elimination | ~0.015% BAC per hour |
What a standard drink is
One US standard drink is about 14 grams of pure alcohol — roughly a 12 oz (355 ml) regular beer, a 5 oz (150 ml) glass of wine, or a 1.5 oz (44 ml) shot of spirits. Cocktails and craft beers often contain more than one.
Why it’s only an estimate
The Widmark model is a simplification. Food in the stomach, the rate of drinking, body composition, liver health, hormones and medications all change real BAC. Two people who drink the same can end up at very different levels. Treat the number as a rough illustration of how alcohol accumulates and clears — nothing more.
Worked example
A 160 lb man who has had 3 standard drinks over the last 2 hours: his weight is about 72,600 g, and with r = 0.68 the peak from 3 drinks is (3 × 14 ÷ (72,600 × 0.68)) × 100 ≈ 0.085%. Subtracting two hours of elimination (2 × 0.015 = 0.03) gives roughly 0.055%. That is only an estimate — and well within the range where driving is impaired and illegal in many places.
FAQ
Can I use this to decide if I can drive?+
No — absolutely not. This is an informational estimate only. Real BAC depends on factors the formula can’t capture, and it can be higher than estimated. If you have consumed any alcohol, the safe choice is not to drive. Impairment begins well below common legal limits.
What is the Widmark formula?+
A long-standing method that estimates BAC from the grams of alcohol consumed divided by body weight times a distribution factor (r), minus the alcohol your liver has eliminated over time (about 0.015% per hour). It gives a ballpark figure, not a measurement.
What counts as one standard drink?+
About 14 grams of pure alcohol — roughly a 12 oz regular beer (5%), a 5 oz glass of wine (12%), or a 1.5 oz shot of spirits (40%). Strong craft beers, large pours and cocktails frequently count as more than one drink.
How long does it take for alcohol to leave my system?+
The body eliminates roughly 0.015% BAC per hour, and that rate can’t be sped up by coffee, food or a cold shower. Only time lowers BAC. The tool shows an estimated time to reach zero, but individual rates vary.
Why do men and women get different results?+
The formula uses a lower distribution factor for women (0.55 vs 0.68), reflecting average differences in body water content. For the same drinks and weight, this generally produces a higher estimated BAC — but it is still only an average, not a personal measurement.