What this calculator does
The Widmark formula estimates blood alcohol from how much alcohol was consumed, how much body water it is distributed through, and how long the liver has had to clear it. It is the basis of most published BAC tables.
It is also a poor guide to any individual. Metabolism, food, medication, hydration and health all shift the real figure substantially, and the formula knows none of them. Treat the output as rough arithmetic about a population, not a measurement of you.
The formula
Alcohol consumed in grams is divided by body weight in grams multiplied by a distribution ratio, then converted to a percentage. Elimination at a steady rate per hour is subtracted for the time elapsed.
| Term | Meaning |
|---|---|
| Widmark factor (r) | The share of body mass that alcohol distributes through: about 0.68 for men, 0.55 for women. |
| Elimination rate | How fast the liver clears alcohol, commonly taken as 0.015 per cent per hour. |
| Standard drink | Varies by country. This calculator works from actual volume and strength instead. |
The inputs explained
| Field | What to enter |
|---|---|
| Drink volume (ml) | Total volume consumed in millilitres at the strength below. For several drinks, enter the combined volume. |
| Alcohol by volume (%) | Alcohol by volume as a percentage. Beer is typically 4 to 6, wine 12 to 14, spirits around 40. |
| Body weight (kg) | Body weight in kilograms. |
| Sex | Sex, which sets the distribution ratio. Body composition differences mean the same drink produces a different concentration. |
| Time since drinking started (hours) | Hours since drinking started, over which elimination has been taking place. |
| Elimination rate (%/hour) | Elimination rate per hour. 0.015 per cent is the usual average, but individuals vary considerably. |
When to use it
Understanding how slowly alcohol clears
Elimination is roughly linear and cannot be accelerated, which is the most useful thing the formula shows.
Seeing why body weight matters
The same drink produces a higher concentration in a smaller person.
Planning the day after
Working out roughly how many hours a heavy evening takes to clear is a legitimate use. Deciding to drive is not.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How long does alcohol take to clear?
The same amount consumed, at four points afterwards.
| Hours elapsed | Estimated BAC | Alcohol consumed |
|---|---|---|
| 1 hour | 0.120% | 69.0 g |
| 2 hours | 0.105% | 69.0 g |
| 3 hours | 0.090% | 69.0 g |
| 6 hours | 0.045% | 69.0 g |
Questions
Can I use this to decide whether to drive?
No. Do not. The estimate can be wrong by a wide margin in either direction, impairment begins below every legal limit, and only a calibrated breath or blood test measures anything real. If you have been drinking, do not drive.
Why does sex change the result?
Alcohol distributes through body water, and body composition differs on average between men and women, which changes the concentration the same dose produces. The factors used here are population averages and will not describe any particular person well.
Does coffee, food or a cold shower speed it up?
No. Elimination happens in the liver at a roughly fixed rate. Food eaten before drinking slows absorption, which lowers the peak, but nothing clears alcohol already in the blood any faster. Only time works.
Why is the formula so unreliable?
It uses population-average constants for distribution and elimination, both of which vary substantially between individuals and within the same person on different days. It also assumes absorption is complete, which it may not be while still drinking.
For body water, which is what alcohol distributes through, see the total body water calculator. For fat-free mass, see the lean body mass calculator.