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Blood Alcohol Content (BAC) Calculator

Estimate your blood alcohol level based on what you've had to drink. Know your limits, plan ahead, and stay safe.

Affects the Widmark r factor: Male = 0.68, Female = 0.55. Women typically have a higher BAC per drink due to body composition.
3 drinks
1 20

1 standard drink = 12oz beer, 5oz wine, or 1.5oz liquor

2 hours
0.5 hr 12 hrs

Your Estimated BAC

0.00

SOBER

BAC Impairment Scale

0.00 – 0.029 Subtle effects, minimal impairment. You may feel normal.
0.03 – 0.059 Mild relaxation, slight euphoria, lowered inhibitions.
0.06 – 0.079 Judgment and reasoning affected. Reduced coordination.
0.08 – 0.099 Legally drunk in the US. Balance, speech, and reaction time impaired.
0.10 – 0.149 Significant impairment of motor control. Slurred speech, poor balance.
0.15 – 0.199 Serious impairment. Risk of blackout, nausea, loss of muscle control.
0.20 – 0.249 Dangerous. Confusion, vomiting, risk of injury or aspiration.
0.25+ Life-threatening. Loss of consciousness, alcohol poisoning. Call 911.

Understanding Blood Alcohol Content

The Widmark Formula

This calculator uses the Widmark formula, a well-established method for estimating blood alcohol content developed by Swedish physician Erik Widmark in the 1930s. It remains the standard approach used in forensic toxicology.

The formula accounts for the amount of pure alcohol consumed (each standard drink contains about 14 grams), your body weight, a sex-based distribution ratio (the Widmark r factor: 0.68 for men, 0.55 for women), and the time elapsed while your liver metabolizes alcohol at roughly 0.015% BAC per hour.

The result is an estimate. Real BAC depends on many individual factors this formula cannot capture, so always err on the side of caution.

What Affects Your BAC Besides Drinks

Food intake: Drinking on an empty stomach can produce a BAC up to 3 times higher than drinking after a full meal. Food slows gastric emptying, giving your liver more time to process alcohol before it reaches your bloodstream.

Medications: Many common medications — including antihistamines, antidepressants, painkillers, and antibiotics — can amplify the effects of alcohol or slow its metabolism. Always check drug interactions.

Hydration: Dehydration concentrates alcohol in your blood. Alternating alcoholic drinks with water can slow absorption and reduce peak BAC.

Tolerance vs. BAC: Regular drinkers may feel less impaired, but their BAC is just as high. Tolerance changes how drunk you feel, not how drunk you actually are. This is one of the most dangerous misconceptions about alcohol.

Body composition: Muscle tissue contains more water than fat tissue. At the same weight, someone with more muscle mass will generally have a lower BAC because alcohol distributes through water in the body.

BAC and Driving

In the United States, the legal limit for drivers 21 and over is 0.08% BAC in all 50 states. For commercial drivers it's 0.04%, and for drivers under 21, most states enforce zero-tolerance policies (0.00–0.02%).

International limits vary significantly. Many European countries set the limit at 0.05%, while countries like Sweden, Poland, and Norway use 0.02%. Some countries — including the Czech Republic, Hungary, and several Middle Eastern nations — enforce a strict 0.00% limit.

Impairment begins well below the legal limit. Studies show that reaction time and divided attention are measurably impaired at BAC levels as low as 0.02%. At 0.05%, the risk of a crash is roughly double that of a sober driver.

The safest choice is always to not drive after drinking. Use a rideshare, call a cab, or designate a sober driver. No estimate can guarantee you are safe to drive.

Frequently Asked Questions

How accurate is a BAC calculator?
BAC calculators use the Widmark formula, which provides a reasonable estimate. However, actual BAC varies based on genetics, liver function, food intake, medications, and other factors. This is an estimate — not a breathalyzer.
What BAC level is legally drunk?
In most US states, the legal limit is 0.08%. However, impairment begins well below that level. Many countries use lower limits (0.05% or even 0.02%).
How long does it take to sober up?
Your body eliminates alcohol at approximately 0.015% BAC per hour (roughly one standard drink per hour). Nothing speeds this up — not coffee, cold showers, or food. Only time works.
Why does weight affect BAC?
Alcohol distributes through body water. Larger people have more body water to dilute the alcohol, resulting in a lower BAC from the same number of drinks.

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Track your BAC in real time with Rebuild

Log drinks, watch your BAC drop, and see exactly when you'll be clear.

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