Blood Alcohol Estimator
An educational estimate of blood alcohol concentration (BAC) using the Widmark formula. This does not make drinking safe.
How to use
- Enter your details and drinks honestly.
- Click Calculate for an educational BAC estimate.
- Remember: the only safe BAC for driving is zero.
For information only — not medical advice. This is a simplified estimate; individual variation is very large (food, metabolism, medication, body composition). Never rely on it to decide whether you can drive — if you have been drinking, do not drive. Consult a healthcare professional for personal guidance.
What Is a Blood Alcohol Estimator?
Blood alcohol concentration (BAC) is the percentage of your blood that is alcohol, and it is the number laws use to define impairment — in most of the United States the legal driving limit is 0.08%, with lower limits for commercial and young drivers, and many other countries set 0.05% or less. This estimator uses the Widmark formula to approximate your BAC from what you drank, your body weight, your gender, and the time elapsed. It is an educational estimate only: real BAC varies widely between individuals, and the only safe BAC for driving is 0.00.
Alcohol does not distribute evenly through the body. It dissolves in body water but not in fat, which is why body weight and gender matter so much: the same drinks produce a higher concentration in a smaller body, and on average in women, whose bodies carry a lower proportion of water than men's.
How to Use the Blood Alcohol Estimator
- Select your gender and enter your body weight (kg or lb).
- Choose the drink type — beer, wine, and a standard shot each count as one standard drink (about 14 grams of pure alcohol); a strong mixed drink counts as about 21 grams.
- Enter how many drinks you have had and over how many hours.
- Click Calculate to see your estimated BAC and how long until it returns toward zero.
The Widmark Formula
Developed by Swedish chemist Erik Widmark in the 1930s, the formula divides the grams of alcohol consumed by the body's effective distribution volume — body weight multiplied by a factor (about 0.68 for men, 0.55 for women) — then subtracts the alcohol eliminated over time. The liver clears alcohol at a fairly steady rate, roughly 0.015 percentage points per hour for most people, which is why only time, not coffee, food, or fresh air, actually lowers BAC after drinking.
Important Safety Notes
- Impairment begins well below the legal limit — judgment and reaction time degrade from the first drink.
- Medications, fatigue, illness, and drinking on an empty stomach can all make real impairment worse than any estimate.
- Never use an estimator to decide whether to drive. If you have been drinking, do not drive — arrange another way home.
How accurate is this estimate?
It is a rough approximation. Food in the stomach, individual liver enzyme levels, body composition, medications, and the actual strength of poured drinks can move a real measurement substantially in either direction. Breathalyzers and blood tests are the only reliable measures; this tool exists for education about how BAC builds and clears.
What is a standard drink?
In the United States, a standard drink contains about 14 grams (0.6 oz) 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 40% spirits. Craft beers, large pours, and mixed drinks often contain considerably more than one standard drink.
How long does alcohol stay in my system?
BAC falls at roughly 0.015 per hour once drinking stops, so someone at 0.08% typically needs five or more hours to reach zero — often well into the next morning after a heavy evening. Detection windows for urine, breath, and hair tests differ and are longer than the impairment window.
Can I speed up becoming sober?
No. The liver metabolizes alcohol at a near-constant rate that coffee, cold air, exercise, vomiting, or food after the fact cannot meaningfully change. Food eaten before or while drinking slows absorption somewhat, which lowers the peak, but once alcohol is in the blood only time removes it.