Can I use this to decide whether to drive?

No. The error band is wider than the margin anyone would be relying on, and the estimate says nothing about impairment, which begins well below any legal limit. If you have been drinking, do not drive.

Does coffee or food bring BAC down?

No. Food slows absorption, so it lowers the peak, and nothing speeds elimination. Coffee makes an intoxicated person alert and intoxicated.

Health & FitnesslifestyleUnited States only

Blood Alcohol Content Calculator

A Widmark estimate of blood alcohol content. It is a population average with an error band wide enough that it cannot tell anyone whether they are fit to drive, and this page will not try.

Also called: blood alcohol calculator, bac estimator.

Estimated BAC

0.05

An estimated 0.05% after 3 standard drinks over 2 hours. Across the plausible range of elimination rates the same drinks give anywhere from 0.027% to 0.057%. That spread is the honest width of this estimate, and it is why the single figure above should not be treated as a measurement. This cannot tell you whether you are fit to drive. Impairment starts below every legal limit, the error band here is wide, and only a calibrated test measures anything. If you have been drinking, do not drive.

Estimated peak, before elimination

0.08

Total alcohol

Hours until it reaches zero

3.15

Low end of the estimate

0.03

High end of the estimate

0.06

How rough this is

Across the plausible range of elimination rates the same drinks give anywhere from 0.027% to 0.057%. That spread is the honest width of this estimate, and it is why the single figure above should not be treated as a measurement.

On driving

This cannot tell you whether you are fit to drive. Impairment starts below every legal limit, the error band here is wide, and only a calibrated test measures anything. If you have been drinking, do not drive.

On the method

Widmark assumes absorption is complete and elimination is constant. Neither holds in the first hour or after a large meal, so the figure is least reliable exactly when people check it.

How this is calculated

For reference only. Verify against your clinical protocol before acting on this number.

Estimated decline over time

Hover or drag for values

Estimated BAC %

Method and background

This is what the calculation gives for the numbers you entered. It is an estimate, not advice, and it knows nothing about your situation beyond those numbers. Rules for United States change on a published schedule; the effective date is shown on every rule-based tool.

How this is calculated

Widmark spreads the alcohol consumed through the body water, approximated as a fixed fraction of body weight, and subtracts a constant elimination rate for time elapsed. Both approximations are crude. The distribution factor varies with body composition rather than sex alone, so it is wrong for anyone whose build differs from the average of the group they were assigned to. Elimination varies between individuals by more than a factor of two, and food, drinking pace, medication and liver function all move the real figure. The page shows a range across plausible elimination rates rather than one number, because the single number is the part people misuse.

the Widmark equation: alcohol spread through the body water fraction, less what has been eliminated since

A: Grams of alcohol
r: Widmark distribution factor
W: Body weight in kilograms
t: Hours elapsed

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

three drinks over two hours

Body weight: 80 kg
Sex: Male
Standard drinks: 3
Alcohol per standard drink: 14 g
Hours since the first drink: 2
Elimination rate: 0.02

Estimated BAC0.05

42 g over 0.68 x 80 kg gives 0.772 g/L, less 0.03 for two hours

Open this example

long enough that it has cleared

Body weight: 80 kg
Sex: Male
Standard drinks: 3
Alcohol per standard drink: 14 g
Hours since the first drink: 8
Elimination rate: 0.02

Estimated BAC0

boundary: elimination has removed more than the peak

Open this example

Method and limits

What it assumes

Drinking is treated as complete, so the estimate applies once absorption has finished.
A constant elimination rate, which is a simplification of a saturable process.

What it deliberately does not model

This is a population estimate and cannot establish an individual BAC. Only a calibrated breath or blood test can.
The distribution factor tracks body composition, not sex, so it is unreliable at either end of the body fat range.
Absorption is not modelled, so the figure is wrong during the first hour and after a large meal.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Can I use this to decide whether to drive?: No. The error band is wider than the margin anyone would be relying on, and the estimate says nothing about impairment, which begins well below any legal limit. If you have been drinking, do not drive.
Does coffee or food bring BAC down?: No. Food slows absorption, so it lowers the peak, and nothing speeds elimination. Coffee makes an intoxicated person alert and intoxicated.