🍺 BAC Calculator: Estimate Your Blood Alcohol Content
By ToolNimba Health Team · Reviewed by ToolNimba Editorial Review, consumer health content · Updated 2026-06-25
This calculator gives a rough estimate only and is not a medical or legal measurement. Real blood alcohol content depends on many factors this tool cannot capture, including food in your stomach, medication, metabolism, body composition, drink strength, and how fast you drank. Never use this estimate to decide whether you are safe to drive or operate machinery. If you have been drinking, do not drive. This is not medical advice.
One US standard drink = 14 grams of pure alcohol (a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot at 40%).
This blood alcohol calculator estimates your BAC, the percentage of alcohol in your bloodstream, using the well known Widmark formula. Enter your sex, body weight, the number of US standard drinks you have had, and how many hours have passed since your first drink. The result is a single estimate to help you understand roughly how alcohol adds up. It is a learning tool, not a breathalyzer, and it must never be used to judge whether you are fit to drive.
What is the Blood Alcohol Calculator?
Blood alcohol content (BAC), also called blood alcohol concentration, is the proportion of alcohol in your blood expressed as a percentage. A BAC of 0.08% means 0.08 grams of alcohol per 100 millilitres of blood, which is the legal driving limit for adults aged 21 and over in most US states. BAC rises while you absorb alcohol and falls as your liver breaks it down at a fairly steady rate, roughly 0.015% per hour for most adults. Because that elimination rate is slow and constant, only time lowers your BAC. Coffee, a cold shower, water, fresh air, and sleep can make you feel more alert, but none of them speed up how fast the liver clears alcohol.
The Widmark formula is the classic way to estimate BAC. It divides the grams of pure alcohol you have consumed by your body water (your weight multiplied by a distribution ratio r), converts that to a percentage, then subtracts the alcohol your body has already cleared based on the hours elapsed. The ratio r reflects the share of the body that is water: it is taken as about 0.68 for men and 0.55 for women on average, because body composition differs between the sexes. The grams of alcohol come from your drink count, where one US standard drink contains 14 grams of pure alcohol. This is the same core method used by calculator.net, Omni Calculator, and most legal and addiction-focused BAC tools online.
The number of standard drinks matters more than the number of glasses. A 12 oz can of regular beer at 5%, a 5 oz glass of table wine at 12%, and a 1.5 oz shot of 40% spirits each contain about 14 grams of alcohol and count as one standard drink. The catch is that real servings are often bigger or stronger. A pint of strong craft beer can be two standard drinks, a large restaurant pour of wine can be one and a half, and a mixed cocktail can hide two or three. Counting servings instead of standard drinks is the single most common reason a real breathalyzer reads higher than people expect.
The most important caveat is that Widmark is a population average, not a personal reading. It assumes one fixed clearance rate and one body water ratio, but real people vary widely. Eating before or while drinking slows absorption and lowers the peak, some medications interact dangerously with alcohol, and metabolism, hydration, age, and body fat all shift the true figure. Two people of the same weight and sex drinking the same amount can land at noticeably different real BAC values, and the difference between a calculated estimate and an actual test can easily cross a legal limit.
It also helps to know how long alcohol stays detectable, which is a separate question from how long you feel drunk. A breath test can detect alcohol for around 12 to 24 hours, a blood test for up to about 12 hours, urine for 12 to 24 hours after light drinking and longer after heavy drinking, saliva for up to about 12 hours, and a hair test for up to roughly 90 days. Feeling sober does not mean your BAC has reached zero, and a hangover can linger long after the alcohol has cleared.
For all of these reasons, treat this calculator as an educational guide to how drinks add up over an evening, not as permission to drive. Legal limits also vary: many US states use 0.08% for drivers 21 and older, Utah uses 0.05%, commercial drivers are often held to 0.04%, and zero-tolerance laws set the limit at 0.00% to 0.02% for drivers under 21. When in doubt, do not drive.
When to use it
- Understanding roughly how several drinks over an evening can add up in your bloodstream.
- Seeing how body weight and sex change the estimated effect of the same number of drinks.
- Learning how the body clears alcohol over time at about 0.015% per hour and roughly how long it takes to reach zero.
- Comparing how a beer, a glass of wine, and a shot of spirits each count as one US standard drink.
- Teaching or studying the Widmark formula in a health, biology, or driver education class.
- Planning a safe ride home in advance by seeing how slowly alcohol leaves the body.
How to use the Blood Alcohol Calculator
- Select your sex, which sets the body water ratio used in the formula.
- Choose your weight unit, then enter your body weight.
- Enter the number of US standard drinks you have consumed (each is 14 grams of alcohol).
- Enter how many hours have passed since your first drink.
- Read the estimated BAC and the impairment band, remembering it is only a rough guide.
Formula & method
Worked examples
A man weighing 80 kg has had 3 standard drinks, and 2 hours have passed since the first.
- Alcohol grams = 3 x 14 = 42 g
- Weight in grams = 80 x 1000 = 80,000 g, and r = 0.68 for men
- Body water term = 80,000 x 0.68 = 54,400
- Raw fraction = 42 / 54,400 = 0.00077206
- As a percent = 0.00077206 x 100 = 0.077206%
- Subtract clearance = 0.077206 - (0.015 x 2) = 0.077206 - 0.03 = 0.047206
Result: Estimated BAC ~ 0.047%
A woman weighing 60 kg has had 2 standard drinks, and 1 hour has passed since the first.
- Alcohol grams = 2 x 14 = 28 g
- Weight in grams = 60 x 1000 = 60,000 g, and r = 0.55 for women
- Body water term = 60,000 x 0.55 = 33,000
- Raw fraction = 28 / 33,000 = 0.00084848
- As a percent = 0.00084848 x 100 = 0.084848%
- Subtract clearance = 0.084848 - (0.015 x 1) = 0.084848 - 0.015 = 0.069848
Result: Estimated BAC ~ 0.070%
How long until that woman reaches a BAC of zero, starting from 0.070%?
- The liver clears alcohol at about 0.015% per hour
- Time to clear = current BAC / clearance rate = 0.070 / 0.015
- Time to clear = about 4.7 hours from the moment of that reading
- Add the 1 hour already elapsed to get roughly 5.7 hours total from the first drink
Result: About 4 to 5 more hours before BAC returns to zero, and longer if more drinks are added
Estimated BAC for a 70 kg (154 lb) man, 1 hour after the first drink
| Standard drinks | Alcohol (grams) | Estimated BAC |
|---|---|---|
| 1 | 14 g | 0.014% |
| 2 | 28 g | 0.044% |
| 3 | 42 g | 0.073% |
| 4 | 56 g | 0.103% |
| 5 | 70 g | 0.132% |
General impairment guide by BAC band (effects vary widely between people)
| BAC range | Typical effects |
|---|---|
| 0.01% to 0.03% | Little to no obvious effect for most people |
| 0.03% to 0.06% | Mild relaxation, slight loss of judgment, lowered inhibition |
| 0.06% to 0.10% | Reduced coordination, slower reaction time, at or above the common 0.08% legal limit |
| 0.10% to 0.20% | Slurred speech, poor balance, impaired vision, possible nausea |
| 0.20% to 0.30% | Confusion, disorientation, vomiting, may need help to stand |
| 0.30% and above | Potentially life threatening, risk of unconsciousness and alcohol poisoning |
What counts as one US standard drink (each about 14 grams of pure alcohol)
| Drink type | Typical strength | One standard drink |
|---|---|---|
| Regular beer | About 5% ABV | 12 oz (355 ml) |
| Malt liquor | About 7% ABV | 8 to 9 oz (240 to 265 ml) |
| Table wine | About 12% ABV | 5 oz (148 ml) |
| Fortified wine | About 17% ABV | 3 to 4 oz (90 to 120 ml) |
| Distilled spirits | About 40% ABV (80 proof) | 1.5 oz (44 ml) shot |
US legal BAC limits and how long alcohol stays detectable
| Topic | Typical value |
|---|---|
| Drivers 21 and over (most states) | 0.08% legal limit |
| Utah legal limit | 0.05% |
| Commercial drivers | 0.04% in most states |
| Drivers under 21 (zero tolerance) | 0.00% to 0.02% |
| Breath test detection window | About 12 to 24 hours |
| Blood and saliva detection window | Up to about 12 hours |
| Urine detection window | 12 to 24 hours, longer after heavy use |
| Hair test detection window | Up to about 90 days |
Common mistakes to avoid
- Treating the estimate as a real reading. The Widmark formula is a population average, not a breathalyzer. Your true BAC depends on food, medication, metabolism, and body composition, so the number here can be well off for any individual and could easily fall on the wrong side of a legal limit.
- Miscounting standard drinks. A large cocktail, a strong craft beer, or a generous pour can each be two or more standard drinks. One US standard drink is 14 grams of alcohol, so heavier pours add up faster than the count suggests. Count standard drinks, not glasses.
- Assuming coffee, water, or a shower lowers BAC. Only time clears alcohol from your blood, at roughly 0.015% per hour. Coffee, cold showers, water, fresh air, and sleep do not speed up the liver, they just may make you feel more alert while still impaired.
- Confusing feeling sober with being sober. The buzz fades long before your BAC reaches zero. You can feel fine the morning after and still have measurable alcohol in your system, which is why morning-after driving arrests happen.
- Ignoring how fast you drank. Drinking the same amount quickly produces a higher peak BAC than spacing it out, because absorption can outpace elimination. The Widmark estimate assumes a single elapsed time and does not capture binge patterns.
- Using the result to decide whether to drive. No estimate is accurate enough to clear you to drive. If you have been drinking, the only safe choice is not to drive, regardless of what any calculator shows.
Glossary
- BAC
- Blood alcohol content, also called blood alcohol concentration, the percentage of alcohol in your blood, for example 0.08%.
- Standard drink
- A defined amount of alcohol. In the United States one standard drink contains 14 grams of pure alcohol.
- Widmark formula
- A classic equation that estimates BAC from alcohol consumed, body weight, sex, and time elapsed.
- Distribution ratio (r)
- The fraction of body weight that is water, taken as about 0.68 for men and 0.55 for women.
- Elimination rate
- How fast the body clears alcohol, on average about 0.015% BAC per hour.
- ABV
- Alcohol by volume, the percentage of a drink that is pure alcohol, such as 5% for regular beer or 40% for spirits.
- Zero tolerance law
- A law that sets a very low legal BAC limit, usually 0.00% to 0.02%, for drivers under the age of 21.
- Alcohol poisoning
- A dangerous, potentially fatal condition that can occur at very high BAC, marked by confusion, vomiting, slow breathing, and unconsciousness.
Frequently asked questions
How is BAC calculated?
This tool uses the Widmark formula: BAC% = (grams of alcohol / (body weight in grams x r)) x 100 minus 0.015 times the hours elapsed. The grams of alcohol come from your drink count (14 grams per US standard drink), and r is 0.68 for men or 0.55 for women.
Is this BAC calculator accurate?
No calculator can give an accurate personal BAC. The Widmark formula is a population average that ignores food, medication, metabolism, drink strength, and body composition. Treat the result as a rough learning estimate only, never as a real measurement, and assume your true BAC could be higher.
Can I use this to decide if I am safe to drive?
Never. The estimate is not precise enough to clear anyone to drive, and your true BAC could be much higher than shown. If you have been drinking, do not drive. Use a taxi, rideshare, public transport, or a sober driver instead.
How long does it take for BAC to reach zero?
The body clears alcohol at roughly 0.015% per hour, so a BAC of 0.06% would take about four hours to fall to zero and a BAC of 0.08% about five hours. A BAC of 0.20% can take 12 to 14 hours. This rate varies between people, and nothing but time reliably lowers it.
What counts as one standard drink?
In the United States one standard drink is 14 grams of pure alcohol, which is about a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot of 40% spirits. Larger or stronger servings count as more than one.
Why does sex change the result?
The formula uses a body water ratio that differs by sex on average, about 0.68 for men and 0.55 for women, because body composition differs. A lower ratio means alcohol is spread through less body water, which tends to raise the estimated BAC for the same number of drinks.
What is the legal BAC limit for driving?
In most US states the limit is 0.08% for drivers aged 21 and over, while Utah uses 0.05% and commercial drivers are often held to 0.04%. Drivers under 21 face zero-tolerance limits of 0.00% to 0.02%. Limits differ by country, so always check local law.
How long does alcohol stay in your system?
It depends on the test. A breath test can detect alcohol for about 12 to 24 hours, blood and saliva for up to about 12 hours, urine for 12 to 24 hours (longer after heavy drinking), and a hair test for up to about 90 days. Detection time is separate from how long you feel impaired.
Does eating before drinking lower your BAC?
Food in your stomach slows how fast alcohol is absorbed, which lowers and delays your peak BAC. It does not reduce the total amount of alcohol your body must process, so it does not speed up how quickly you sober up. The Widmark formula does not account for food.
Can coffee or a cold shower sober me up faster?
No. Only time lowers your BAC, at roughly 0.015% per hour. Coffee, cold showers, water, exercise, and fresh air may make you feel more awake, but you remain just as impaired. A wide-awake drunk is still drunk.
Sources
- Understanding the Dangers of Alcohol Overdose , National Institute on Alcohol Abuse and Alcoholism (NIAAA)
- Impaired Driving: Get the Facts , U.S. Centers for Disease Control and Prevention (CDC)