Knowing roughly how much alcohol is in your bloodstream before you make a decision can keep you, your passengers, and everyone else on the road safe. This blood alcohol calculator estimates your blood alcohol content (BAC) using the classic Widmark equation — the same model forensic toxicologists use to back-estimate BAC from a drink log. It factors in your biological sex, body weight, the total pure alcohol you have consumed, and how much time has passed, then estimates when your body will clear the alcohol.
Move the sliders and the result updates instantly. A glass of wine and a shot are not the same amount of pure alcohol, so enter the actual ounces of ethanol rather than the number of glasses; the section below explains how to estimate it from beer, wine, and liquor.
How to Use
- Choose your Biological Sex — male or female. This sets the Widmark distribution factor (r), because women and men distribute alcohol into body water differently on average.
- Enter your Body Weight in pounds. Heavier people dilute the same amount of alcohol across more tissue, which is why two people drinking identical rounds can end up at different BAC levels.
- Set Pure Alcohol Consumed to the total fluid ounces of ethanol, not the size of the drink container. A standard US drink is about 0.6 fl oz (14 g) of pure alcohol — roughly a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot of 80-proof liquor. Multiply your drink count by 0.6 to get a reasonable starting value.
- Enter Time Since Drinking Began in hours. The calculator subtracts the alcohol your liver has already eliminated, roughly 0.015% BAC per hour.
- Read the result card: your estimated BAC, how many more hours it will take to reach zero, the equivalent number of standard US drinks, the grams of pure alcohol you consumed, and your driving status code under the 0.08% threshold used in most US states (0 = under 0.05%, 1 = 0.05–0.08%, 2 = at or over 0.08%).
The estimate is an average across a population. Real BAC varies with food in the stomach, medications, hydration, genetics, and how fast you drank, so treat the number as a planning guide rather than a breathalyzer reading.
The Widmark Formula
Your estimated BAC comes from the Widmark equation:
BAC = (A × 5.14) / (W × r) − 0.015 × t
Where:
- A is the pure alcohol consumed in fluid ounces.
- W is your body weight in pounds.
- r is the Widmark factor — about 0.73 for men and 0.66 for women on average.
- t is elapsed time in hours.
- The 0.015 is the typical hourly elimination rate (about 0.015% BAC per hour).
The 5.14 constant converts ounces of ethanol into the percentage units breathalyzers report. Worked example: a 180 lb man who drinks 2.0 fl oz of pure alcohol over one hour gets (2.0 × 5.14) / (180 × 0.73) − 0.015 = 0.063%. After two more hours the same drinks fall to about 0.033%, because the liver keeps removing alcohol while no new drinks arrive.
If the math drives the result below zero, the calculator clamps it to 0.000% — you are sober, and drinking coffee or a cold shower will not speed that up.
What Affects Your Real BAC
The formula uses averages, and your actual number can move well outside them:
- Sex and body water. Women typically carry a lower fraction of body water and more body fat, so the same drinks produce a higher peak BAC. That is why r is 0.66 rather than 0.73.
- Food. A full stomach slows gastric emptying and flattens the peak. Drinking on an empty stomach hits harder and faster.
- Rate of consumption. Chugging three drinks in 30 minutes peaks higher than spreading them over three hours, even though the total alcohol is identical.
- Medications and health. Sleep aids, opioids, cannabis, and some cold medicines multiply impairment long before they move the BAC number. Liver disease slows elimination.
- Proof and pour. A "standard" restaurant wine pour is often 6–8 oz, and a free-poured shot is often 2 oz. Real-world drinks usually exceed the 0.6 fl oz assumption.
Because these factors are invisible to the calculator, build in a safety margin: stop earlier than the math suggests, and never rely on an estimate to decide whether to drive.
Examples
Example 1 — A night out for one person. A 180 lb man drinks the equivalent of three to four standard beers (about 2.0 fl oz pure alcohol ≈ 3.3 standard drinks ≈ 47 g of ethanol) over one hour. The formula gives about 0.063% BAC — under the 0.08% limit but already legally impaired in many contexts, and close enough to the line that one more drink could cross it. Time to sober up: roughly 4.2 hours from now. The driving status code reads 1 (0.05–0.08% range).
Example 2 — Lower body weight. A 130 lb woman drinks two glasses of wine (1.2 fl oz) across two hours. Her estimated BAC lands near 0.042%. It looks modest, but after two more hours of no drinking it would fall to about 0.012% — the elimination clock works in your favor the longer you wait.
Example 3 — The 0.08% boundary. On average, a 160 lb man reaches 0.08% after about three to four standard drinks in an hour on an empty stomach; a 130 lb woman reaches it after about two to three. Individual variation is wide, which is why these are planning numbers, not a pass/fail line.
FAQ
How accurate is this blood alcohol calculator?
It uses the Widmark equation, the same model forensic toxicologists rely on, but it is built from population averages. Real BAC typically lands within ±20–30% of the estimate for a given person and can differ more if you ate heavily, took medication, or drank unusually fast. Use it to plan, not to certify sobriety.
What does a BAC of 0.08% mean?
0.08% is the per se driving limit for adults in most US states. At that level reaction time, judgment, and coordination are clearly impaired, and crash risk rises sharply. In some states and for drivers under 21 the limit is lower (0.02–0.05%).
How long until I am sober?
After your last drink, the body eliminates alcohol at roughly 0.015% BAC per hour. This calculator divides your current estimated BAC by 0.015 to project the hours needed to reach zero. A 0.08% peak typically needs about five and a half hours to clear.
Does food or coffee lower my BAC?
Food slows absorption and lowers the peak, but it does not reduce the total alcohol already absorbed. Coffee, exercise, and cold showers do not speed elimination — only time does.
Why do men and women have different results?
The Widmark factor r reflects the fraction of body water alcohol distributes into. On average women have less body water and more body fat per pound, so the same drinks concentrate more in the blood. That is why r is 0.66 for women and 0.73 for men.
How many drinks equal 0.08% BAC?
It depends on weight, sex, and time. Roughly three to four standard drinks in an hour for a 160 lb man, or two to three for a 130 lb woman, put many people near 0.08%. Because variation is large, treat that as an upper planning estimate and stop well before it.
Disclaimer
This blood alcohol calculator is provided for informational purposes only and is not medical advice or a substitute for a calibrated breathalyzer or blood test. Estimates derive from average Widmark parameters and may differ substantially from your actual BAC. Never drink and drive — if you have been drinking, use a rideshare, a designated driver, or wait until you have allowed enough time for your body to clear the alcohol. Consult a qualified healthcare professional for personal guidance on alcohol use, and contact emergency services for any suspected overdose.