Health

Blood Alcohol Calculator

Estimate your blood alcohol content (BAC) using the Widmark formula. See impairment level and estimated time until sober.

Quick Answer

One standard drink (12 oz beer, 5 oz wine, or 1.5 oz spirits) raises BAC by approximately 0.02-0.03% for an average adult. The legal limit in all US states is 0.08%. Your body metabolizes about 0.015% BAC per hour, so a BAC of 0.08 takes roughly 5.3 hours to reach zero.

Estimated BAC

Estimated BAC
0.065%
Legal Status
Impaired driving range (0.05-0.08)
Time Until Sober
4.3 hrs

Impairment Level

Moderate impairment — reduced coordination

BAC Impairment Reference

0.02-0.03%Slight relaxation, mild mood elevation
0.04-0.06%Lowered inhibition, slight impairment of reasoning
0.07-0.09%Impaired balance, speech, reaction time
0.10-0.15%Significant impairment, slurred speech, poor coordination
0.16-0.30%Severe impairment, nausea, disorientation
0.30%+Risk of loss of consciousness, life-threatening
Safety Warning: This calculator provides rough estimates only and should NEVER be used to determine if you are safe to drive. Many factors affect BAC that this tool cannot account for, including food intake, medications, tolerance, liver health, and rate of consumption. The only safe amount of alcohol before driving is zero. If you have been drinking, use a designated driver, rideshare, or taxi. If you suspect alcohol poisoning (confusion, vomiting, seizures, slow breathing), call 911 immediately.

About This Tool

Blood Alcohol Content (BAC) measures the percentage of alcohol in your bloodstream. This calculator uses the Widmark formula, the same mathematical model used by forensic toxicologists and law enforcement since the 1930s. While no calculator can replace a breathalyzer or blood test, understanding the factors that influence BAC can help you make more informed decisions about alcohol consumption.

The Widmark Formula

The Widmark formula calculates BAC as: BAC = (alcohol consumed in grams / (body weight in grams × r)) × 100 - (0.015 × hours). The "r" value is the Widmark factor: 0.68 for males and 0.55 for females. This difference exists because females typically have a higher body fat percentage and lower body water content, leading to higher BAC from the same amount of alcohol.

Metabolism Rate

The average person metabolizes alcohol at about 0.015% BAC per hour, which equates to roughly one standard drink per hour. This rate is relatively constant and cannot be sped up by coffee, cold showers, or exercise. Some individuals metabolize slightly faster (up to 0.020%) or slower (down to 0.010%) depending on genetics, liver size, and enzyme activity.

Factors This Calculator Cannot Account For

Food intake significantly slows alcohol absorption; drinking on an empty stomach can result in a BAC 2-3 times higher than drinking after a full meal. Medications, including acetaminophen and antihistamines, can intensify impairment. Fatigue, stress, and dehydration all worsen the effects of alcohol at any BAC level. Individual tolerance affects perceived impairment but does NOT change actual BAC or legal status.

Frequently Asked Questions

How many drinks does it take to reach 0.08% BAC?
For an average 170 lb male, roughly 4 standard drinks in one hour will reach approximately 0.08%. For a 140 lb female, it takes approximately 3 drinks. However, this varies significantly based on food intake, rate of drinking, and individual metabolism.
Does coffee sober you up?
No. Coffee may make you feel more alert, but it does not reduce BAC or improve impairment. Only time reduces BAC as your liver metabolizes the alcohol. A wide-awake drunk is still a drunk. The only cure for intoxication is time.
Why do women get higher BAC than men from the same number of drinks?
Women typically have higher body fat percentage and lower body water than men at the same weight. Since alcohol is water-soluble, it concentrates in less body water, resulting in a higher BAC. Women also produce less alcohol dehydrogenase, the stomach enzyme that breaks down alcohol before it reaches the bloodstream.
How long should I wait after drinking to drive?
A general guideline is one hour per standard drink, plus one additional hour for safety. However, this is only approximate. If your BAC was 0.08%, you would need roughly 5-6 hours to fully sober up. When in doubt, do not drive.
Can you fail a breathalyzer the morning after drinking?
Yes. If you drank heavily the night before and stopped at midnight with a BAC of 0.15%, you might still have a BAC of 0.06% at 6 AM. Heavy drinking sessions can leave residual BAC well into the next morning. For every 0.015% BAC, you need about one additional hour.

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