Blood Alcohol Calculator: Estimate Your BAC
Our blood alcohol calculator estimates your BAC from your weight, your sex, the drinks you had and the hours since your first drink. It also shows how long the alcohol may take to leave your system. Use this BAC calculator for planning and learning only, because it is not a legal test.
What Is Blood Alcohol Concentration?
Blood alcohol concentration, or BAC, is the share of alcohol in your blood. A BAC of 0.08% means 0.08 grams of alcohol in every 100 milliliters of blood. Doctors, police and breath devices all report it in the same units.
A blood alcohol calculator cannot measure your blood. It uses a formula built on averages, so the answer is an estimate. Real readings can differ a lot from one person to the next.
How to Use the BAC Calculator
- Choose US pounds or metric kilograms, then enter your weight.
- Pick your sex, because the body water ratio differs.
- Enter the hours since your first drink.
- Choose each drink type and how many you had. The custom row takes a drink with its own size and strength.
The results show your BAC now, the peak before any elimination, standard drinks, and the time until you are under 0.08, under 0.05 and back at zero. A table lists the estimate hour by hour. Change any field and the BAC calculator updates every number at once.
How the Blood Alcohol Calculator Works
The tool uses the Widmark formula, developed by the Swedish scientist Erik Widmark. First it adds up the grams of pure alcohol, which is volume in milliliters times strength times 0.789. Next it divides by body weight in grams times a ratio called r, then multiplies by 100. Finally it subtracts 0.015 for each hour that has passed.
| Item | Value used |
| Alcohol density | 0.789 g per ml |
| Ratio r for men | 0.68 |
| Ratio r for women | 0.55 |
| Elimination rate | 0.015 BAC per hour |
| One US standard drink | 14 g of pure alcohol |
The ratio r reflects how much of your body weight is water, where alcohol spreads. Women tend to have a lower ratio, so the same drinks give a higher reading. The elimination rate is an average, and studies report a range of roughly 0.010 to 0.020 per hour.
Standard Drinks in the BAC Calculator
| Drink | Size | Strength | Pure alcohol |
| Beer | 12 oz | 5% | 14.0 g |
| Wine | 5 oz | 12% | 14.0 g |
| Spirits | 1.5 oz | 40% | 13.9 g |
| Strong beer | 12 oz | 8% | 22.4 g |
The BAC calculator presets follow the US standard. The first three each hold about 14 grams of alcohol, which counts as one standard drink. A large pour or a strong craft beer can count as two.
Blood Alcohol Content Calculator Examples
Three Beers in Two Hours
A 180 pound man has three 12 ounce beers at 5%, and two hours pass. The drinks hold 42 grams of alcohol, which is 3.0 standard drinks. His peak is 0.076% and the estimate now is 0.046%. The tool shows about 3 hours and 3 minutes before he reaches zero.
Two Glasses of Wine for a Smaller Frame
A 140 pound woman drinks two 5 ounce glasses of wine, and one hour passes. The peak is 0.080% and the estimate now is 0.065%. She would need about 4 more hours and 21 minutes to reach zero.
Five Shots over Three Hours
A 200 pound man takes five 1.5 ounce shots of 40% spirits over three hours. The peak without elimination is 0.113% and the estimate now is 0.068%. That pace gives a far higher number than the beer example, even with the same time passing.
BAC Levels and What They Mean
| BAC | Typical effects |
| 0.02 to 0.03 | Mild relaxation and slightly slower reactions |
| 0.04 to 0.06 | Lower caution and poorer judgment |
| 0.08 | Legal limit for adult drivers in most US states |
| 0.10 to 0.15 | Clear loss of balance, speech and vision |
| 0.16 to 0.24 | Severe impairment, vomiting and blackouts |
| 0.25 and above | Medical danger because breathing can fail |
These bands are general, and people react differently. A blood alcohol level calculator cannot see your tolerance or health. Utah and Scotland use 0.05, and many countries set 0.05 or lower. No amount of drinking is guaranteed safe behind the wheel.
How to Calculate BAC by Hand
You can check the blood alcohol calculator with a pencil. Divide the grams of alcohol by your weight in kilograms times 1000 times r, then multiply by 100. Subtract 0.015 for every hour since the first drink, and a result below zero means the alcohol is gone. Any BAC calculator follows this same arithmetic.
Why Your Real BAC May Differ
- Food slows absorption and lowers the peak.
- Medicines, tiredness and illness change how you feel at the same level.
- Drinking pace matters, because a blood alcohol level calculator treats all drinks as one amount.
- Large pours often hold more alcohol than the label size.
Every blood alcohol calculator also assumes an average body. Muscle, fat and hydration all shift the ratio. Because of these limits, treat the answer as a rough guide.
Safety and Legal Notes
Do not use any blood alcohol calculator to decide whether you can drive. Police use breath or blood tests, and the law looks at your actual reading. If you have been drinking, wait, take a taxi or ask a sober friend to drive. Call a doctor or emergency services if someone cannot stay awake after drinking.
Why Use Our BAC Calculator
It shows BAC now, the peak, standard drinks and the time to zero in one view. You can add four drink types, including a custom pour. Enter your details and check your estimate now.
Frequently asked questions
Is this BAC calculator accurate?
It gives a Widmark estimate, so real BAC can differ.
What is the legal BAC limit?
It is 0.08% for adult drivers in most US states and 0.05% in Utah.
How long does it take to sober up?
The body clears about 0.015 BAC per hour, so a 0.06 reading needs roughly 4 hours.
Does this blood alcohol content calculator work for women?
Yes, it uses a lower ratio of 0.55 for women.
Can coffee or a cold shower lower my BAC?
No, only time removes alcohol from your blood.
Is the blood alcohol calculator free?
Yes, it is free and runs in your browser.
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