Blood Alcohol Content Calculator
The Widmark BAC formula is used by law enforcement and health researchers to estimate blood alcohol concentration from the number of drinks consumed and key personal factors. This calculator provides an estimate for educational purposes only — never drive based on a formula result.
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Formula
BAC = (Drinks × 14) ÷ (Weight_kg × r) − 0.015 × Hours
Each standard drink contains 14 g of pure alcohol. The Widmark r factor — 0.68 for males and 0.55 for females — represents the fraction of body mass that is water, since alcohol distributes into water. Body weight is converted from lbs to kg by multiplying by 0.454. BAC decreases at 0.015% per hour as the liver metabolizes approximately one standard drink per hour.
How to use the Blood Alcohol Content Calculator
- 1
Enter your number of drinks
- 2
Enter your body weight
Value should be in lbs.
- 3
Enter your gender
- 4
Enter your hours since first drink
Value should be in hours.
- 5
Read your results instantly
Results update in real time as you type.
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What BAC levels mean
BAC of 0.02–0.03%: Mild relaxation, slight impairment of judgment. BAC of 0.05–0.08%: Noticeable impairment of judgment, coordination, and reaction time. Legal driving limit in most US states is 0.08%. BAC of 0.08–0.15%: Significant impairment, slurred speech, balance problems. BAC of 0.15–0.25%: Severe impairment, disorientation. BAC above 0.25%: Risk of alcohol poisoning, unconsciousness, and respiratory depression. BAC above 0.40% can be fatal. Individual sensitivity varies considerably with tolerance, age, and medications.
Why this is an estimate only
The Widmark formula is a population average with individual variation of ±20–30%. Food in the stomach significantly slows alcohol absorption. Medications, hormones, hydration, and genetic differences in alcohol dehydrogenase enzyme activity all affect actual BAC. Breathalyzer readings and blood draws are the only legally reliable BAC measurements. This calculator is purely educational — never drive after drinking, regardless of what any formula says. The only safe BAC for driving is 0.00%.
Tips & Insights
One standard drink takes about one hour to metabolize
The liver processes roughly 0.015% BAC per hour. You cannot speed up this process with coffee, water, food, or exercise — only time reduces BAC.
Food slows but does not prevent intoxication
Eating before and during drinking slows alcohol absorption, keeping peak BAC lower and more delayed. It does not reduce the total alcohol in your system.
Women are generally more affected than men
Women typically have lower body water percentage and lower alcohol dehydrogenase activity, leading to higher BAC per drink than men of the same weight.
Worked Examples
160 lb male, 2 drinks in 1 hour
Estimated BAC ≈ 0.040%
130 lb female, 3 drinks in 2 hours
Estimated BAC ≈ 0.077%
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Frequently Asked Questions
What counts as a standard drink?
In the US, one standard drink contains 14 g of pure alcohol: 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz distilled spirits (40%).
Can I drive if my calculated BAC is below 0.08%?
No. Even at 0.02–0.05% BAC, reaction time and judgment are measurably impaired. The legal limit is not a safety threshold — it is an enforcement threshold. The safest choice is not to drive after any drinking.
How long does alcohol stay in your system?
Detection depends on the test: breath and blood tests detect alcohol for 12–24 hours; urine tests for 12–48 hours (or up to 80 hours with EtG tests); hair follicle tests for up to 90 days.
Does tolerance affect BAC?
Tolerance affects how impaired you feel at a given BAC but does not meaningfully change the BAC itself. A person with high tolerance may feel sober at 0.10% BAC but is equally impaired in measurable tasks.
Is this formula used by law enforcement?
The Widmark formula is used in forensic and research contexts, but law enforcement relies on breathalyzers and blood draws for legally admissible BAC measurements.
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