How to use the BAC calculator
- 1 Choose your sex and enter your body weight.
- 2 Enter the number of standard drinks.
- 3 Enter the hours since your first drink.
- 4 Read your estimated BAC, what it means and how long until it reaches zero.
Worked example
A 180-pound man who had 4 standard drinks over 2 hours. 4 drinks contain 56 g of alcohol. The peak estimate is 56 ÷ (81,647 g × 0.68) × 100 = 0.101%; after removing 0.015% per hour for 2 hours, the estimated BAC is 0.071%, over Utah's 0.05% limit and impaired. It would take about 4.7 more hours to reach zero. Do not drive after drinking.
Drinking more safely
- Never drive after drinking, whatever the estimate.
- Count real drinks: many pours are more than one standard drink.
- Eat and drink water, but know they do not speed sobering.
- Call 911 for signs of alcohol poisoning.
See how body size is measured with the BMI Calculator and Body Surface Area Calculator, and convert your weight with the Weight Converter.
Features
Widmark formula
The standard method behind BAC estimates.
Time to sober
Hours until 0.00% at an average 0.015% per hour.
Legal limits shown
0.08% in most US states, 0.05% in Utah.
When to use it
Understanding drinks
See how quickly standard drinks add up for your body weight.
Planning a safe ride home
Use it as a reminder to arrange a ride, never as permission to drive.
Health awareness
Pair with the Calorie Calculator: alcohol has 7 calories per gram.
Education
Learn how weight, sex and time change BAC.
Related Health and Fitness tasks
Frequently asked questions
How is BAC calculated?
With the Widmark formula: BAC = alcohol in grams ÷ (body weight in grams × r) × 100, minus about 0.015% for each hour since drinking began. r is about 0.68 for men and 0.55 for women.
What is a standard drink?
In the US, a drink with 14 grams of pure alcohol: 12 oz of regular beer (5%), 5 oz of wine (12%) or 1.5 oz of 80-proof spirits (40%). Many drinks served are larger.
What is the legal BAC limit for driving?
0.08% in every US state except Utah, where it is 0.05%. It is 0.04% for commercial drivers, and drivers under 21 face zero-tolerance limits of 0.00% to 0.02%.
How long does it take for BAC to reach zero?
The body removes about 0.015% per hour on average, roughly one standard drink an hour. A BAC of 0.08% takes over 5 hours to clear. Coffee, water and showers do not speed it up.
Is this calculator accurate?
It is an estimate. Food, drinking speed, medication, health and genetics change real BAC, sometimes a lot. Only a breath or blood test measures it.
Why does sex affect BAC?
On average, women have a lower share of body water than men of the same weight, so the same alcohol gives a higher concentration.
Can I drive if the calculator shows under 0.08%?
No. Impairment begins well below 0.08%, and the estimate can be wrong. If you have been drinking, use a designated driver, a taxi or public transport.
What are the effects at different BAC levels?
Around 0.02% judgment and relaxation change; at 0.05% coordination and alertness drop; at 0.08% control and reaction are clearly impaired; at 0.15% there is major loss of balance; 0.30% and above can be life-threatening.
What are signs of alcohol poisoning?
Confusion, vomiting, seizures, slow or irregular breathing, blue or pale skin, low body temperature and not waking up. Call 911 (or your local emergency number) immediately.
Does eating before drinking help?
Food slows absorption and lowers the peak, but it does not stop alcohol from reaching your blood or speed up its removal.
Does body weight change BAC?
Yes. A heavier person has more body water to dilute the same alcohol, so the same drinks give a lower BAC.
Built and reviewed by Hamza Farooq, founder and lead developer
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