Calculate This Body · BAC
Module · Body

Blood Alcohol
Estimator

Estimated BAC from drinks, weight, sex, and time elapsed. Includes time-to-sober projection. This is a rough estimate - do not use it to decide whether to drive.

See the math behind this calculator
Legal limit (US)
0.08% BAC

Commercial drivers
0.04%

Utah, several countries
0.05%
You
Drinks
Timeline
Estimated BAC 0.00%
Status-
Below 0.08% in-
Fully sober in-
Pure alcohol (oz)-

The Widmark formula

BAC estimates use the Widmark equation, developed in the 1930s. It's the same math driving every BAC calculator and breathalyzer-prediction app.

BAC = (oz_alcohol × 5.14 / weight_lb × r) − (0.015 × hours)

Where r is the distribution ratio - about 0.68 for men, 0.55 for women on average, reflecting differences in body water content. The 0.015 per hour is the average elimination rate; your liver clears about one standard drink per hour.

Frequently asked

How accurate is this?

For an average person of average size with average metabolism, it's within about ±0.02 of a measured BAC. Outliers are common. Asians, women, the elderly, anyone on medications, and people with liver issues clear alcohol differently. The only way to know your real BAC is to test it.

Can I drive at 0.05%?

In most US states, the legal limit is 0.08%, but driving impairment starts well before that. Studies show reaction time slows by 15-20% at 0.05%. Several countries set the limit at 0.05% for that reason. Even at 0.03%, you're a statistically worse driver than sober.

Does coffee, food, or a shower sober me up?

No. Nothing speeds alcohol metabolism. Coffee makes you feel more alert without lowering your BAC - which is dangerous, because you think you're fine when you're not. Time is the only thing that sobers you up. About one hour per standard drink.

What about edibles and cannabis?

This calculator only models ethanol. Mixing alcohol with cannabis, opioids, or sedatives compounds impairment in ways the math here doesn't capture. Don't drive on combinations.

Show the working

This is the Widmark equation, unchanged since the 1930s. It is the same model behind every BAC estimator, and its limitations are structural rather than a fault of this page. If any of it looks wrong, it might be - tell us what we got wrong.

Alcohol consumed fl oz alcohol = sum over each drink of volume in oz × (ABV ÷ 100)
Peak BAC peak = (fl oz alcohol × stomach factor × 5.14) ÷ (body weight lb × r)
Elimination over time BAC = peak − (0.015 × hours since first drink) floored at zero
Time projections hours to below 0.08 = (BAC − 0.08) ÷ 0.015 hours to zero = BAC ÷ 0.015

Constants used

  • 5.14 — Widmark's conversion constant for ounces of alcohol, pounds of body weight and percent BAC
  • r = 0.68 / 0.55 — body water distribution ratio, male and female averages
  • 0.015 per hour — average elimination rate, roughly one standard drink an hour
  • 1.15 — multiplier applied for an empty stomach, an approximation of faster absorption

Everything above is an average applied to an individual, which is exactly the situation where averages fail. Genetics, medication, food, hydration and liver function all move the real number, and the model assumes instant absorption it does not have. Do not use this to decide whether to drive.

The sources

This page implements the Widmark equation, which is the basis of essentially every BAC estimate including the ones used forensically. It is nearly a century old and its limits are well documented, so the sources below are as much about the error bars as the formula.

Widmark, as implemented here BAC = (oz of alcohol x 5.14 / (weight lb x r)) - (0.015 x hours)
  1. Guidelines for estimating the amount of alcohol consumed from a single measurement of blood alcohol concentration: re-evaluation of Widmark's equation. Forensic Sci Int, 1995. The modern re-evaluation of the equation, and the source for treating r as a population average with real spread rather than a fixed personal constant.
  2. Alcohol calculations and their uncertainty. Medicine, Science and the Law - PubMed Central, NIH. Quantifies how much uncertainty a Widmark estimate actually carries. The most useful single source here for understanding why this page shows a figure and not a verdict.
  3. The estimation of blood alcohol concentration: Widmark revisited. Forensic Science, 2015. Where the 0.68 male and 0.55 female r values come from, and why they are averages of a distribution rather than constants.
  4. The impact of total body water on breath alcohol calculations. PubMed Central, NIH. Body water is what r is standing in for, and this is what happens to the estimate when an individual's body water differs from the average the r value assumes.
  5. Experimental study of the temporal profile of breath alcohol concentration after a light meal. PubMed Central, NIH. Measured food effects on absorption, which is the closest published support for the empty-stomach adjustment on this page.

Two honest weak points. The 0.015 per hour elimination rate is a median - the published range runs roughly 0.010 to 0.020, so the time-to-sober figure can be out by a third in either direction. And the 1.15 empty-stomach multiplier is an approximation of a real effect rather than a published coefficient; food changes the shape of the absorption curve, not just its height. Nothing here should be used to decide whether to drive.