BAC Calculator - Blood Alcohol Content
Estimate your blood alcohol content using the medically validated Widmark formula. Enter your sex, weight, the drinks you consumed, and how long you have been drinking. The calculator shows your current BAC, how long until you are sober, when you fall below the legal driving limit, the full BAC timeline, and a breakdown of the effects at your level. Switch between metric and imperial units and choose your jurisdiction for the correct legal limit.
Formula
Worked example
A 160 lb (72.6 kg) male drinks 2 standard beers (355 mL at 5%) over 1 hour. Pure alcohol = 2 x 355 x 0.05 x 0.789 = 28.0 g. Peak BAC = 28.0 / (0.68 x 72.6) x 100 = 0.566%. After 1 hour of elimination: 0.566 - (0.015 x 1) = 0.551%. Time until sober from that point: 0.551 / 0.015 = about 36.7 more hours.
How this BAC calculator works
This calculator uses the Widmark formula, the most widely cited method for estimating blood alcohol content. You enter your biological sex, body weight, the number and type of drinks consumed, and the time since your first drink. The formula converts each drink to grams of pure ethanol (volume times ABV times alcohol density, 0.789 g/mL), sums them, then divides by the product of your body water constant (the Widmark r-factor) and your weight. That gives peak BAC in percent. The calculator then subtracts the amount eliminated at a standard rate of 0.015% per hour to give your current estimated BAC. Time until sober is current BAC divided by 0.015.
The Widmark r-factor and why sex matters
The Widmark r-factor reflects the proportion of the body that is water, because alcohol distributes in body water. Males average about 0.68 and females about 0.55, because females typically have a higher proportion of body fat and lower total body water for the same weight. This single difference means a woman and a man of equal weight who drink the same amount will have meaningfully different BAC values, with the woman reaching a higher peak. Body composition varies between individuals, so the r-factor is an average; lean or very muscular people will be slightly above the average, and those with higher body fat slightly below.
How the body eliminates alcohol
The liver processes most ingested alcohol at a fairly constant rate regardless of how much you have consumed, averaging about 0.015% BAC per hour for most adults, with a typical range of 0.010% to 0.020% depending on genetics, liver health, and regular drinking habits. Unlike most drugs, alcohol metabolism follows zero-order kinetics, meaning the body clears a fixed amount per unit time rather than a fixed fraction. This is why the timeline to sobriety scales linearly with peak BAC. Nothing speeds the process: cold water, coffee, vomiting, and sleep do not increase the elimination rate, though sleep is still safer than driving while impaired.
Legal limits and why they vary
Most US states and Canada use 0.08% as the legal blood alcohol limit for driving. Australia, New Zealand, and much of continental Europe use 0.05%, reflecting research showing significant driving impairment at that level. Sweden, Norway, and Poland use 0.02%. The stricter limits align with evidence that risk of a fatal crash approximately doubles at 0.05% and is around seven times higher at 0.08% compared to a sober driver. Being below the legal limit does not mean you are unimpaired: reaction time, divided attention, and hazard perception are measurably worse even below 0.05%.
BAC levels and effects
| BAC (%) | Impairment level | Typical effects |
|---|---|---|
| 0.001-0.029 | Minimal | Average person appears normal; subtle effects detectable by testing only |
| 0.030-0.059 | Mild | Mild euphoria, relaxation, talkativeness; concentration begins to decline |
| 0.060-0.099 | Moderate | Blunted feelings, impaired depth perception, peripheral vision, reaction time |
| 0.100-0.199 | Significant | Slurred speech, staggering, impaired reflexes and gross motor control |
| 0.200-0.299 | Severe | Nausea, vomiting, emotional swings, possible blackout, memory loss |
| 0.300-0.399 | Life-threatening | Stupor, loss of consciousness, low possibility of death |
| 0.400+ | Potentially fatal | Coma, severe CNS depression, high risk of death |
General effects at each BAC range. Individual responses vary with tolerance, food intake, and other factors.
Frequently asked questions
How accurate is the Widmark BAC formula?
The Widmark formula is the best widely available estimate, but it is not a precise measurement. It uses population-average constants that do not account for individual variation in body composition, liver enzyme activity, gut absorption rate, or the presence of food. Actual BAC measured by a breathalyzer or blood draw can be 10-30% higher or lower than the estimate. Use this tool to understand approximate impairment levels and safe drinking windows, not to decide whether you are safe to drive.
Does food affect BAC?
Yes, significantly. Food in the stomach slows gastric emptying and delays alcohol absorption into the bloodstream, lowering the peak BAC and spreading it out over a longer period. Fatty foods have the biggest buffering effect. This calculator does not model food intake because the size and timing of meals vary too much to include accurately. If you have eaten a full meal, your actual peak BAC will likely be lower and arrive later than the estimate.
Can I sober up faster with coffee or a cold shower?
No. Coffee and cold showers make you feel more alert, but they do not change how fast your liver processes alcohol. Your BAC follows the same elimination curve regardless. Appearing more awake while still impaired can actually be more dangerous because it creates false confidence about driving ability.
What is a standard drink?
In the United States, one standard drink contains 14 grams of pure alcohol. This equals roughly 355 mL (12 oz) of regular beer at 5%, 148 mL (5 oz) of wine at 12%, or 44 mL (1.5 oz) of spirits at 40% ABV. Many craft beers, large wine pours, and mixed cocktails contain significantly more than one standard drink, so counting "drinks" without knowing ABV and volume can underestimate actual alcohol intake.
Why does BAC differ between men and women of the same weight?
Alcohol distributes in body water, not total body mass. Women typically have proportionally more body fat and less body water than men of the same weight, so the same amount of alcohol is distributed in a smaller water compartment and produces a higher concentration. The Widmark formula captures this with different r-factors: 0.68 for males and 0.55 for females.
How long does alcohol stay in your system?
At a standard elimination rate of 0.015% per hour, a person who reaches a peak BAC of 0.15% will take about 10 hours to reach zero. A breathalyzer can detect alcohol for up to 24 hours after drinking. Blood tests can detect it for around 12 hours, urine tests for up to 24-48 hours, and hair follicle tests for up to 90 days. These detection windows are longer than the impairment window.
Sources
- Widmark EMP (1932). Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. Urban and Schwarzenberg, Berlin.
- National Institute on Alcohol Abuse and Alcoholism. Alcohol Metabolism: An Update.
- NHTSA Traffic Safety Facts: Alcohol-Impaired Driving (2022)