Blood alcohol concentration estimate (Widmark) — weight & time in any unit.
BAC = (A × 5.14 / W × r) − (0.015 × T)
The most widely used method for estimating BAC is the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s. It accounts for the total alcohol consumed, a person's body weight, a biological sex-based distribution factor (r), and the amount of alcohol already metabolized over time.
The formula calculates the peak BAC from alcohol intake and then subtracts the alcohol eliminated by the body at a constant metabolic rate (approximately 0.015 g/dL per hour).
BAC = (1.8 × 5.14 / 180 × 0.73) − (0.015 × 2) = (9.252 / 131.4) − 0.030 = 0.0704 − 0.030 = 0.040 g/dL
Result: Estimated BAC ≈ **0.04 g/dL**
A BAC of 0.04 g/dL falls below the US legal driving limit of 0.08 g/dL. However, even at this level, the CDC notes that judgment, tracking ability, and reaction time may be mildly impaired. The individual in this example should still exercise caution before driving. Had only 1 hour elapsed instead of 2, the estimated BAC would be approximately 0.055 g/dL — still below the legal limit but with more noticeable impairment. This is an estimate only. Actual BAC can differ due to food intake, medication, hydration, liver health, and individual metabolic variation.
BAC (Blood Alcohol Concentration) measures how much ethanol is present in your bloodstream. It is expressed as grams of alcohol per 100 mL of blood (g/dL) or equivalently as a percentage. A BAC of 0.08% means 0.08 grams of alcohol per 100 mL of blood — the legal per se driving impairment threshold in all 50 US states and many countries worldwide.
After drinking, ethanol is rapidly absorbed through the stomach and small intestine into the bloodstream, typically reaching peak blood levels within 30–90 minutes on an empty stomach. The liver then breaks down alcohol at a relatively constant rate — approximately one standard drink per hour — primarily via the enzyme alcohol dehydrogenase (ADH). Unlike most substances, the body cannot speed up this process; drinking coffee, eating food, or exercising after drinking will not significantly accelerate sobering up.
| BAC (g/dL) | Typical Effects | |---|---| | 0.02–0.03 | Mild relaxation, slight mood elevation | | 0.04–0.06 | Reduced inhibition, mild impairment of judgment | | 0.07–0.09 | Impaired balance, speech, vision, reaction time; legally drunk in most jurisdictions | | 0.10–0.12 | Significant motor impairment, slurred speech | | 0.13–0.15 | Gross motor impairment, severe lack of judgment | | 0.16–0.19 | Dysphoria, nausea possible | | 0.20+ | Confusion, stupor, risk of blackout | | 0.30+ | Risk of loss of consciousness | | 0.40+ | Potentially fatal — respiratory depression |
Most countries set the legal blood alcohol limit for driving at 0.05–0.08 g/dL. Several countries (Sweden, Japan, Czech Republic) use a limit as low as 0.02 g/dL. Commercial drivers in the US face a stricter limit of 0.04 g/dL.
This calculator is intended for educational and harm-reduction purposes only. It is not a medical device and cannot replace a certified breathalyzer or blood test. Individual BAC may differ substantially from this estimate. Never drive after drinking, regardless of your estimated BAC. If you or someone you know may be experiencing alcohol poisoning, call emergency services (911 in the US) immediately.
Drinking water does not meaningfully lower your BAC, but it helps prevent dehydration and may reduce next-day hangover symptoms. Water does not accelerate the liver's metabolism of ethanol — only time does.
They are closely related but not identical. Breath alcohol concentration (BrAC) is measured in grams per 210 liters of breath. Breathalyzers use a blood-to-breath ratio of approximately 2,100:1 to convert BrAC to an equivalent BAC. This ratio varies slightly between individuals and can affect breathalyzer accuracy.
Eating before or during drinking significantly slows alcohol absorption by delaying gastric emptying. A full stomach can reduce peak BAC by 30–50% compared to drinking on an empty stomach. The Widmark formula does not account for food intake — actual BAC on a full stomach will typically be lower than the calculator's estimate.
For an average 160 lb male, a BAC of 0.10 g/dL roughly corresponds to consuming about 4–5 standard drinks within one hour. For an average 130 lb female, it might be reached with just 3–4 standard drinks in the same timeframe. Results vary substantially with body weight, time, and individual metabolism.
Medications do not change your measured BAC, but many drugs — including antihistamines, benzodiazepines, opioids, antidepressants, and sleep aids — can dramatically amplify the impairing effects of alcohol at any given BAC level. Always consult a pharmacist or physician about drug-alcohol interactions.
The Widmark formula provides a reasonable estimate but is not perfectly precise. Studies show the formula can vary by ±10–15% from actual measured BAC due to individual differences in metabolism, body composition, stomach contents, and hydration. Use it as a guide, not a definitive measurement.
One standard US drink contains 14 grams (0.6 fl oz) of pure ethanol. This is equivalent to: a 12 oz regular beer (5% ABV), a 5 oz glass of wine (12% ABV), or a 1.5 oz shot of distilled spirits (40% ABV / 80 proof).
No. This calculator is for educational purposes only. It cannot tell you whether it is safe or legal to drive. Perceived impairment, reaction time, and judgment can be significantly reduced even at BAC levels below the legal limit. If you have been drinking, the safest choice is not to drive.
The body eliminates alcohol at roughly 0.015 g/dL per hour. A person with a BAC of 0.08 g/dL would take approximately 5–6 hours to reach 0.00 g/dL. Time is the only reliable way to lower BAC — coffee, water, food, and exercise do not speed up elimination.
Biological females generally have a higher body-fat-to-water ratio and lower levels of the enzyme alcohol dehydrogenase in the stomach lining. This means less alcohol is broken down before it enters the bloodstream, and the same amount of alcohol is distributed in a smaller volume of body water — resulting in a higher BAC compared to a male of the same weight.
In all 50 US states, a BAC of 0.08 g/dL or higher is the legal per se limit for non-commercial drivers aged 21 and over. Commercial vehicle operators face a stricter limit of 0.04 g/dL, and drivers under 21 are subject to zero-tolerance laws (typically 0.00–0.02 g/dL depending on the state).
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