How to Use Our BAC Calculator
This tool uses the widely accepted Widmark formula to estimate your BAC. For an accurate result, please provide the following information as honestly as possible.
Gender: Select Male or Female. This is a crucial biological factor, as men and women metabolize alcohol differently due to variations in body water content and enzyme levels.
Weight: Enter your current body weight in pounds (lb) or kilograms (kg). Your weight determines how much water is in your body, which affects how diluted the alcohol becomes in your bloodstream.
Number of Standard Drinks: This is the most important input. It is critical to count your drinks correctly. A “standard drink” in the United States is defined as any beverage containing 0.6 ounces (14 grams) of pure alcohol.
1 Standard Drink = 12 oz of regular beer (~5% alcohol)
1 Standard Drink = 5 oz of table wine (~12% alcohol)
1 Standard Drink = 1.5 oz of 80-proof distilled spirits (gin, rum, vodka, whiskey) (~40% alcohol)
Be aware that many craft beers, cocktails, and generous wine pours contain more than one standard drink. For example, a 12 oz IPA at 9% ABV is roughly 1.7 standard drinks.
Time Since Last Drink (in hours): Enter the total time that has passed since you finished your last alcoholic beverage. Your body begins metabolizing alcohol as soon as you start drinking, and this input accounts for the alcohol that has been eliminated from your system over time.
Understanding Your Results
Legal Disclaimer: This calculator provides an estimate for educational and informational purposes only. It is not a legal definition or a substitute for an official breathalyzer or blood test. The results should not be used to determine whether it is safe for you to drive or operate machinery. Individual metabolism, food consumption, medications, and other factors can alter your actual BAC. If you have been drinking, the only safe choice is to not drive.
Your result is your estimated Blood Alcohol Content (BAC), expressed as a percentage. This percentage represents the weight of ethanol in grams per 100 milliliters of blood. For example, a BAC of 0.08% means your blood is 0.08% alcohol by volume.
BAC Levels, Effects, and Impairment
The legal limit for driving in all 50 U.S. states (except Utah, where it is 0.05%) is 0.08%. However, impairment begins at much lower levels.
Frequently Asked Questions
How does food in my stomach affect my BAC?
Eating food before or while drinking, especially food high in protein, fat, and fiber, can significantly slow down the absorption of alcohol into your bloodstream. It doesn’t stop the alcohol from being absorbed, but it spreads the absorption over a longer period. This results in a lower peak BAC compared to drinking on an empty stomach. Drinking on an empty stomach allows alcohol to pass quickly from the stomach to the small intestine, where it is absorbed rapidly, leading to a much faster and higher spike in BAC.
Why do gender and weight matter so much in BAC calculation?
These are two of the most important factors:
Weight: Alcohol is water-soluble. A heavier person has more body water than a lighter person of the same gender. This larger volume of water dilutes the alcohol more, resulting in a lower BAC for the same number of drinks.
Gender: Women generally have a higher percentage of body fat and a lower percentage of body water than men of the same weight. Because alcohol resides in body water, a woman’s BAC will be higher than a man’s after consuming the same amount of alcohol. Additionally, men have higher levels of an enzyme called alcohol dehydrogenase (ADH) in their stomachs, which begins breaking down alcohol before it even reaches the bloodstream.
How fast does my BAC go down?
On average, the body metabolizes and eliminates alcohol at a rate of about 0.015% per hour. This means that if your BAC is 0.10%, it would take over 6 hours for it to return to 0.00%. This rate is relatively constant for most people and cannot be sped up. Nothing you do—drinking coffee, taking a cold shower, exercising—will make you sober up faster. Only time can lower your BAC.
What does “one standard drink” really mean at a bar or party?
This is where most people miscalculate their intake. A “standard drink” is a precise measurement (1.5 oz of spirits, 5 oz of wine, 12 oz of beer).
A cocktail often contains 2-3 ounces of spirits, making it 1.5-2 standard drinks.
A bartender’s “generous” pour of wine might be 7-9 ounces, not 5 ounces.
Many popular craft beers, like IPAs and stouts, have a higher alcohol by volume (ABV) than “regular” beer. A 12 oz, 8% ABV beer is equivalent to about 1.6 standard drinks. Always be mindful of the actual alcohol content and serving size, not just the number of glasses you’ve had.
Can I really get a DUI if my BAC is under 0.08%?
Yes. While 0.08% is the per se legal limit (meaning you are considered intoxicated by law regardless of evidence), you can still be arrested and convicted of a DUI/DWI in most states if a law enforcement officer can prove that your driving ability was impaired to any degree by alcohol, even with a BAC below 0.08%. Furthermore, for commercial drivers, the limit is 0.04%, and for drivers under 21, all states have “Zero Tolerance” laws, where any detectable amount of alcohol (typically 0.01% or 0.02%) is illegal.
What are the legal consequences of a DUI?
The consequences of a first-offense DUI (Driving Under the Influence) or DWI (Driving While Intoxicated) are severe and vary by state, but they typically include:
License Suspension: Usually from 90 days to one year.
Fines and Fees: Often totaling thousands of dollars when court costs, legal fees, and administrative fees are included.
Jail Time: Possible, even for a first offense, ranging from a few days to several months.
Ignition Interlock Device (IID): A device installed in your car that requires you to pass a breath test before the engine will start.
Increased Insurance Rates: Your car insurance premiums will rise dramatically for several years.
A Permanent Criminal Record: This can affect employment, housing, and professional licenses.
How accurate are personal breathalyzers?
The accuracy of personal breathalyzers varies wildly. High-quality, fuel-cell sensor models (the same technology used in police devices) can be reasonably accurate if properly calibrated and used correctly. However, cheaper, semiconductor-based models can be highly unreliable and affected by things like smoke, food, or even breath fresheners. They should be used for informational purposes only and never be trusted to make a decision about driving.
What is a “blackout” and how is it different from “passing out”?
Passing Out: This is losing consciousness due to high levels of alcohol sedation. The person is asleep and cannot be easily awakened. This is a sign of a dangerously high BAC.
Blackout: This is a period of alcohol-induced amnesia. The person is conscious, walking, talking, and interacting with others, but the brain is not forming long-term memories. They will have little to no recollection of events the next day. Blackouts typically occur at BAC levels of 0.16% and higher and are a sign of binge drinking.
Concrete Example: A Night Out
Let’s track a hypothetical person’s BAC:
Person: A 180 lb male.
8:00 PM: He has his first 12 oz, 5% beer. (1 standard drink)
9:00 PM: He has a second beer. (2 total drinks)
10:00 PM: He has a strong cocktail with 2 oz of whiskey. (This is ~1.3 drinks, bringing his total to 3.3 standard drinks). He finishes this drink at 10:30 PM.
11:30 PM: It has been one hour since his last drink.
Calculation:
Inputs: Male, 180 lbs, 3.3 drinks, 1 hour since last drink.
Estimated BAC: The calculator would estimate his BAC to be around 0.065%.
Interpretation: While he is below the 0.08% legal limit, his judgment and reaction time are already impaired. It would be unsafe for him to drive. To be safe, he would need to wait approximately 4-5 more hours without drinking for his BAC to approach zero.
Why do I feel drunker than my BAC estimate, or vice-versa?
Feeling “drunk” is subjective. Your perceived level of intoxication can be influenced by tolerance (a regular drinker may not “feel” a 0.08% BAC), fatigue, mood, and expectations. However, your actual physiological impairment is directly related to your BAC. Even if you don’t feel drunk, your reaction time, coordination, and judgment are impaired at a BAC of 0.08%, which is why the limit is based on this objective measurement. Never trust how you feel over your estimated BAC.
Understanding the effects of alcohol is the first step toward responsible consumption. For more information on what constitutes a serving size, see this detailed guide on Understanding Standard Drinks. Making a plan before you start drinking is the best way to ensure a safe night for yourself and others.
