BAC Calculator
Estimate your blood alcohol concentration (BAC) from your sex, body weight and what you drank, see how long it takes to return to about zero, and compare the figure with the limits used for driving. This is an estimate, not a measurement — never use it to decide whether to drive.
This is an estimate from a population formula (Widmark), not a measurement, and it must not be used to decide whether you are safe or legal to drive. Food in the stomach, body composition, medication, liver health and genetics all move the real number, and absorption is incomplete for up to an hour after the last drink. The formula also assumes you drank at an even pace. If you have been drinking, do not drive — the only reliable answers come from a breath or blood test. The limits in the table are the commonly quoted ones; they vary by state, country and driver category, and they change — check the current law where you drive.
Formula and calculation
Worked example
A man weighing 72.6 kg (160 lb) who drinks four 355 ml beers at 5% over two hours: that is 56.02 g of pure alcohol, or about 4 US standard drinks. Before elimination his BAC works out to 0.106, and after two hours of clearance at 0.015 per hour the estimate is 0.0757 — above the 0.05 limit used in much of Europe and in Scotland, though under the 0.08 limit that applies in most US states, England and Wales. At that rate it would take about 5 h 3 min to return to about zero.
What the estimate cannot see
Two people with identical sex, weight and drinks can differ by 0.02 or more on a breath test. Food in the stomach slows absorption; a full stomach spreads the peak out and flattens it. Body composition matters as much as weight — the formula uses total kilograms, but alcohol only distributes into body water, so the same weight in fat and muscle gives different results. Medication, liver health, drinking frequency, menstrual cycle, hydration and genetics each move the number too. Absorption also takes 30 to 90 minutes, so within the first hour after a drink the real value may be lower than the estimate and still climbing. That is why a single number from a calculator should never sit between you and a decision about driving.
What the results mean
- Estimated blood alcohol
- Your estimated blood alcohol concentration, in percent — grams of alcohol per 100 mL of blood. Most US states set the adult driving limit at 0.08; many other countries use 0.05 or 0.02. This is a population formula's estimate and can be off by a wide margin for any one person.
- Time until your BAC returns to about zero
- Roughly how long until the estimate falls back to about zero, at the average elimination rate of 0.015 per hour that Widmark-style estimators use. Real clearance runs between 0.010 and 0.020 per hour, so the true time can be half or double this figure.
- Pure alcohol consumed
- Total grams of pure alcohol in everything you entered. A US standard drink holds about 14 g, whatever the glass looks like.
- Standard drinks
- Your total converted into US standard drinks of 14 g each — useful when you mixed drinks of different strengths.
Frequently asked questions
Can I use this estimate to decide whether I am safe to drive?
No. This is a rough estimate from a population formula, not a measurement of you, and it can understate the real figure. Limits also differ by state and country, and some places prosecute from 0.02 or zero. If you have had anything to drink, do not drive — use a taxi, public transport or a sober driver. Only a breath or blood test measures BAC.
How long does alcohol stay in your system?
Alcohol clears at roughly 0.015 per hour on average — some people 0.010, others 0.020 — so a BAC of 0.08 usually takes around five hours to reach zero, and a heavy night can still show alcohol the next morning. One standard drink adds around two hours of clearance for a 70 kg man and closer to three for a smaller woman. Nothing speeds the liver up.
Does coffee, a shower or fresh air sober you up?
No. They can make you feel more awake, which is worse than useless because alertness is not sobriety — reaction time, judgment and coordination stay impaired. The liver clears alcohol at its own fixed pace, and only time reduces BAC. Eating before or during drinking slows absorption, but it does not sober you up afterwards.
How much does one drink raise my BAC?
One US standard drink — a 355 ml beer, a 148 ml glass of wine or a 44 ml shot — raises BAC by roughly 0.02 to 0.03 for an average-size man and 0.03 to 0.04 for a smaller woman. Two drinks therefore put many people at or above 0.05, and three get a lighter person near 0.08.
Why is the estimate different from my breathalyzer result?
The formula assumes average absorption, average body water and an average elimination rate, and it ignores food, medication, drinking speed and your individual metabolism. A breath test measures actual alcohol in your breath. Where the two disagree, the measurement is right and the estimate is wrong — and courts, insurers and employers all treat the measurement as the real number.