Alcohol units calculator
Estimate alcohol intake and blood alcohol concentration with the Widmark equation: enter volume, ABV, body weight, sex and hours since drinking to get ethanol grams, US standard drinks (14 g), UK units (8 g), peak and current BAC, and the hours needed to sober up.
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Drinking data
Widmark equation: BAC(%) = ethanol grams ÷ (weight kg × r × 10) − 0.015 × hours, with r = 0.68 for men and 0.55 for women.
Result
13.0 g0.93 drinks1.63 units0.0273 %0.0273 %0.273 ‰1.82 h1.82 hWhat this tool does
- Work out how many standard drinks a 500 mL bottle of beer or a glass of wine really is, so you can compare it with official low-risk drinking limits.
- Estimate your peak BAC before a night out and see why the same two drinks hit a lighter person — or a woman — harder.
- Compare drinks: enter volume and ABV to see how 330 mL of beer stacks up against 150 mL of wine in grams of ethanol.
- Estimate how long until you are back to zero, so you book a taxi or stay over instead of guessing.
Example
Input
Volume 330 mL, ABV 5 % vol, weight 70 kg, male, 0 hours since drinking started
Output
Pure ethanol 13.0 g; 0.93 US standard drinks; 1.63 UK units; peak BAC 0.0273 %; current BAC 0.0273 % (0.273 ‰); 1.82 hours from peak to zero; 1.82 hours back to zero
Widmark equation: BAC(%) = ethanol grams ÷ (weight kg × r × 10) − 0.015 × hours, with r = 0.68 for men.
Frequently asked questions
How is BAC calculated?
With the Widmark equation: pure ethanol grams = volume × ABV × 0.789 g/mL; the peak is that divided by (weight kg × distribution factor r × 10), and the current value subtracts 0.015% per hour elapsed. The distribution factors r = 0.68 for men and 0.55 for women come from Widmark’s 1932 work.
Why is BAC higher for women?
Women generally have a lower proportion of body water and a higher proportion of body fat, so the volume alcohol distributes into is smaller and blood concentration is higher for the same intake. The Widmark factor captures this as r = 0.55 versus 0.68, so at equal weight and intake the estimated peak is roughly 24% higher.
Can I use this to decide whether I can drive?
No. The formula assumes complete absorption, an empty stomach and a steady elimination rate, while real life involves drinking speed, food, liver health, medication and individual variation — a fast drink on an empty stomach can peak far higher than the estimate. Never drive after drinking; take a taxi, public transport or stay the night.
What is the difference between a standard drink and a UK unit?
A US standard drink is 14 g of pure ethanol (NIAAA), roughly a 355 mL beer at 5%, a 150 mL glass of 12% wine or a 44 mL shot of 40% spirits. A UK unit is 8 g, so the same drink counts almost twice as high in units. Both numbers are shown so you can compare with guidance from either country.
What is the difference between “peak to zero” and “time back to zero”?
The first is the total elimination time from the peak and depends only on intake and body weight. The second starts from the hours-since-drinking you entered, so it shrinks as time passes. Reaching zero only means the formula hits zero — hangover effects and slower reactions can linger.
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