🍺 BAC Calculator
Estimate blood alcohol concentration from drinks, weight, sex and time with the Widmark formula, plus a range and time to zero. Not for driving decisions.
Drinks
Between 0.05 and 0.08 — above Utah’s legal driving limit, and impairment is measurable.
This is a rough estimate, not a measurement. Food, medications, health, genetics and how quickly you drank all change real BAC. Never use it to decide whether you can drive — if you have been drinking, do not drive.
What BAC Calculator Does
This BAC calculator estimates blood alcohol concentration from what you drank, your body weight, sex and the time since your first drink, using the Widmark formula that underlies most published BAC charts. Add each drink by size and alcohol percentage — a 16 oz IPA is not the same as a 12 oz light beer — and the calculator converts it to grams of alcohol and U.S. standard drinks.
Because people clear alcohol at different speeds, the result is shown as a central estimate and a likely range, along with an estimate of how long until alcohol is fully eliminated. It is a teaching and awareness tool: the formula cannot account for food, medications, health or genetics, and real BAC can differ a lot from any calculator.
It must never be used to decide whether you are fit to drive. Impairment starts well below the legal limit, and the only safe BAC for driving is zero.
How to Use BAC Calculator
- Choose sex and enter your body weight
- Enter the hours since your first drink
- Add each drink — how many, the size in ounces and the % alcohol
- Read the estimated BAC, the likely range and time to zero
- Treat it as an estimate only — do not use it to decide to drive
Formula Used by BAC Calculator
Widmark formula
BAC (%) = A ÷ (W × r) × 100 − β × t
- A
- Alcohol consumed, in grams (volume × ABV × 0.789 g/mL)
- W
- Body weight, in grams
- r
- Distribution ratio: about 0.68 for men, 0.55 for women
- β
- Elimination rate: about 0.015 % per hour on average
- t
- Hours since the first drink
Worked example
A 180 lb (81.6 kg) man, four 12 oz beers at 5%, over 2 hours.
- Alcohol: 4 × 355 mL × 0.05 × 0.789 = 56 g
- 56 ÷ (81,647 g × 0.68) × 100 = 0.101%
- 0.101 − 0.015 × 2 = 0.071%
Result: About 0.071% — impaired, and above Utah’s 0.05% limit.
What Counts as One U.S. Standard Drink (14 g of alcohol)
| Drink | Typical alcohol | One standard drink |
|---|---|---|
| Regular beer | 5% | 12 fl oz |
| Malt liquor | 7% | 8–9 fl oz |
| Table wine | 12% | 5 fl oz |
| Distilled spirits (80 proof) | 40% | 1.5 fl oz |
BAC and U.S. Driving Limits
| BAC | What it means |
|---|---|
| Any amount | Drivers under 21: zero-tolerance laws apply |
| 0.04% | Legal limit for commercial vehicle drivers |
| 0.05% | Legal limit for drivers in Utah |
| 0.08% | Legal limit in every other state |
How to Read Your Result
Why the range matters
The same drinks can leave two people of the same weight at noticeably different levels. Elimination commonly varies between people and even day to day, and drinking on an empty stomach produces a faster, higher peak. The upper end of the range is the more cautious number to keep in mind.
Only time lowers BAC
Coffee, cold showers, exercise, food after drinking and sleep do not speed up how fast the liver removes alcohol. They may make someone feel more alert, which is more dangerous, not less. BAC can also keep rising for a while after the last drink as alcohol is absorbed.
Signs of alcohol poisoning
Confusion, vomiting, seizures, slow or irregular breathing, pale or bluish skin, low body temperature, or being hard to wake are emergencies. Call 911, stay with the person, and keep them on their side.
Limitations & Accuracy Notes
- The Widmark formula is an average-person model; body composition, age, food, medications and health conditions all change real BAC.
- It assumes all alcohol was absorbed; shortly after drinking, actual BAC may still be rising.
- This estimate has no legal or medical standing and must not be used to decide whether to drive, operate machinery, or care for others.
Frequently Asked Questions
How is BAC calculated?
How many drinks to reach 0.08?
How long does it take for alcohol to leave your body?
What is the legal limit?
What is a standard drink?
Is this calculator accurate?
References & Further Reading
- NIAAA — What Is A Standard Drink? — 14 grams of pure alcohol per U.S. standard drink