BAC Calculator
Estimate your blood alcohol content based on the number of drinks, your body weight, gender, and how long you've been drinking. See impairment levels and time until sober.
How Blood Alcohol Content Works
Blood alcohol content, usually called BAC, is a measurement of how much alcohol is circulating in your bloodstream at any given moment. It's expressed as a percentage — a BAC of 0.08% means that 0.08 grams of alcohol are present for every 100 milliliters of blood. That doesn't sound like much, and it isn't, but even tiny concentrations of alcohol have real effects on your brain and body.
When you take a drink, alcohol passes through the lining of your stomach and small intestine into the bloodstream. From there it travels throughout your body, including your brain, where it starts affecting judgment, coordination, and reaction time. Your liver breaks it down at a fairly constant rate — about one standard drink per hour for most people — but if you're drinking faster than your body can metabolize, your BAC climbs.
A standard drink is defined as 0.6 ounces of pure alcohol. That translates to roughly 12 ounces of regular beer at 5% ABV, 5 ounces of wine at 12% ABV, or 1.5 ounces of distilled spirits at 40% ABV. These aren't exact for every beverage — a craft IPA might be 7% or 8%, and a generous wine pour at home is often closer to 7 or 8 ounces — but they're the benchmarks that BAC formulas use.
Factors That Affect Alcohol Absorption
Your BAC after a few drinks depends on a lot more than just how many you've had. Body weight is the most obvious factor — a 200-pound person has more blood volume and body water to dilute alcohol compared to someone who weighs 130 pounds. That's why the same three beers hit different people differently.
Biological sex plays a role too, and it's not just about average size differences. Women generally have a higher percentage of body fat and lower percentage of body water than men of the same weight. Since alcohol is water-soluble, it concentrates more in a smaller water volume, leading to higher BAC readings. That's why the Widmark formula uses different distribution constants for men and women.
Food in your stomach matters a great deal. Drinking on an empty stomach means alcohol hits your bloodstream fast because there's nothing to slow absorption. A full meal, especially one with fats and proteins, can significantly slow the rate at which alcohol enters your blood. It won't change your total absorption — you'll still process all the alcohol eventually — but it spreads it out over a longer period, keeping your peak BAC lower.
Other factors include medications, hydration level, fatigue, and individual genetics. Some people produce more of the enzyme alcohol dehydrogenase, which breaks down alcohol in the stomach before it even reaches the bloodstream. Others, particularly some people of East Asian descent, have a genetic variation that makes alcohol metabolism less efficient, leading to faster intoxication and the characteristic facial flushing.
Legal Limits and What They Mean
In the United States, the legal BAC limit for driving is 0.08% in all 50 states. But that number doesn't tell the whole story. Commercial drivers are held to a stricter standard of 0.04%, and for anyone under 21, most states enforce a zero-tolerance policy with limits at 0.01% or 0.02%.
Other countries set their limits differently. Much of Europe uses 0.05%, and some countries — including the Czech Republic, Hungary, and several others — enforce a strict 0.00% limit. There's been a push in the US to lower the limit to 0.05%, and Utah already made that change in 2018.
Here's what's worth understanding: impairment doesn't start at 0.08%. Studies show measurable decreases in reaction time and divided attention at BAC levels as low as 0.02%. By 0.05%, most people have noticeably reduced coordination and judgment. The legal limit is a legal threshold for criminal charges, not a medical determination that you're safe to drive below it.
You should also know that BAC calculators, including this one, provide estimates. Actual BAC depends on your individual metabolism, what you ate, your hydration, medications, and other variables that no formula can fully account for. A breathalyzer or blood test is the only way to know your real BAC. Never rely on a calculator to decide whether you're okay to drive.
Common Myths About Sobering Up
There's no shortage of folk wisdom about how to sober up fast, and almost none of it works. Coffee doesn't reduce your BAC — it just makes you a more alert drunk. Caffeine can mask the drowsy effects of alcohol, which might actually be more dangerous because you feel more capable than you are. Cold showers, exercise, eating after drinking, and splashing water on your face are all equally useless for lowering your blood alcohol level.
The only thing that reduces BAC is time. Your liver metabolizes alcohol at approximately 0.015% per hour, and nothing speeds that up meaningfully. If your BAC is 0.12%, you're looking at roughly 8 hours before you're back to zero. Not 8 hours until you feel fine — 8 hours until the alcohol is actually gone from your blood.
Another persistent myth is that you can beat a breathalyzer by sucking on a penny, chewing gum, or using mouthwash. None of these work, and mouthwash can actually make things worse because many brands contain alcohol. Breathalyzer technology measures deep-lung air and isn't fooled by mouth tricks.
The "I'm a big person so I can handle more" belief has a grain of truth — body weight does dilute alcohol — but it leads people to overestimate their tolerance. A 250-pound man who's had six beers in two hours likely has a BAC around 0.07%, which is below the legal limit but still impaired enough to increase accident risk significantly.
<strong>Important Disclaimer:</strong> This BAC calculator is intended for educational purposes only. It provides rough estimates based on averages and cannot account for your individual metabolism, health conditions, or other factors. Never use a calculator to determine whether it's safe to drive. If you've been drinking, use a designated driver, rideshare service, or taxi. When in doubt, don't drive.
Widmark Formula
BAC = (Drinks × 0.06 × 100) / (Weight × Gender Constant) - (0.015 × Hours)
The Widmark formula is the standard method for estimating blood alcohol content. Each standard drink contains roughly 0.6 ounces of pure alcohol. The formula divides the total alcohol consumed by a factor of body weight and a gender-specific distribution ratio (0.73 for men, 0.66 for women), then subtracts the metabolism rate of 0.015% per hour. For example, a 170-pound man who has had 3 drinks over 2 hours would have an estimated BAC of about 0.047%.
Where:
- BAC = Blood alcohol content as a percentage
- Drinks = Number of standard drinks consumed (each = 0.6 oz pure alcohol)
- Weight = Body weight in pounds
- Gender Constant = 0.73 for males, 0.66 for females (alcohol distribution ratio)
- Hours = Time elapsed since first drink
Example Calculations
Casual Evening Out
A 170-pound man has 3 beers over 2 hours at a bar with friends.
- Drinks consumed: 3 standard drinks
- Body weight: 170 lbs (male)
- Time drinking: 2 hours
- BAC = (3 × 0.06 × 100) / (170 × 0.73) - (0.015 × 2)
- BAC = 18 / 124.1 - 0.03
- BAC ≈ 0.145 - 0.03 = 0.115%
- Status: Above legal limit, impaired coordination
Even three drinks over two hours can put an average-sized man near or above the legal limit. With food in the stomach, actual BAC might be somewhat lower, but it's not worth the risk. This is a good illustration of why "just a few beers" isn't always as harmless as it sounds.
Wine at Dinner
A 140-pound woman has 2 glasses of wine over 3 hours with a meal.
- Drinks consumed: 2 standard drinks
- Body weight: 140 lbs (female)
- Time drinking: 3 hours
- BAC = (2 × 0.06 × 100) / (140 × 0.66) - (0.015 × 3)
- BAC = 12 / 92.4 - 0.045
- BAC ≈ 0.130 - 0.045 = 0.085%
- Status: Near or above legal limit
Two glasses of wine might feel moderate, but for a smaller woman, it can still approach the legal limit. Having food with the drinks helps slow absorption, but doesn't eliminate the alcohol. Waiting an additional hour or two before driving would be the smart move here.
Frequently Asked Questions
BAC calculators provide rough estimates based on average metabolism rates and the Widmark formula. Real-world BAC depends on many individual factors including stomach contents, medications, hydration, liver health, and genetics. Actual BAC can be 20-30% higher or lower than a calculator's estimate. The only accurate way to measure BAC is with a breathalyzer or blood test. Never rely on a calculator to decide if you're safe to drive.
Your body metabolizes alcohol at roughly 0.015% BAC per hour. A single standard drink raises most people's BAC by about 0.02% to 0.04%, so it typically takes about 1 to 2.5 hours for one drink to be fully metabolized. However, this rate is fairly constant regardless of how much you've had. If you've consumed several drinks and your BAC reaches 0.10%, it could take nearly 7 hours to return to 0.00%.
A standard drink in the United States contains approximately 0.6 ounces (14 grams) of pure alcohol. This works out to 12 ounces of regular beer at 5% ABV, 5 ounces of wine at 12% ABV, or 1.5 ounces of distilled spirits at 40% ABV. Craft beers, large wine pours, and strong cocktails often contain more than one standard drink, which is something people frequently underestimate.
Eating food before or while drinking doesn't reduce the total amount of alcohol your body absorbs, but it does slow the rate of absorption. Food in your stomach, especially foods high in protein and fat, keeps the pyloric valve closed longer, which delays alcohol from reaching the small intestine where most absorption occurs. The result is a lower peak BAC spread over a longer period. Eating after you're already intoxicated has minimal effect.
Even at the same weight, women typically reach higher BAC levels than men for several biological reasons. Women generally have a higher ratio of body fat to water. Since alcohol dissolves in water rather than fat, there's less volume to dilute the alcohol, resulting in higher concentrations. Women also tend to produce less of the enzyme alcohol dehydrogenase in the stomach lining, meaning more alcohol passes into the bloodstream intact.