Blood alcohol content (BAC) estimate by the Widmark formula from drinks, body weight and time, with the elimination curve and time back to zero.
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By the Widmark estimate, blood alcohol is about 0.042% now and falls to zero in roughly 2 h 47 min. This is an average-person model, not a measurement.
r = 0.73 for men: the share of body weight that holds the alcohol.
0.015 % per hour is an average elimination rate; individual rates differ.
Blood alcohol content (BAC) is estimated with the Widmark formula: the alcohol drunk is spread through a share r of body weight, 0.73 for men and 0.66 for women, and about 0.015 percentage points are eliminated per hour. In US units, BAC % = fluid ounces of alcohol × 5.14 ÷ (weight in lb × r) − 0.015 × hours. One US standard drink holds 14 g, or 0.6 fl oz, of pure alcohol (NIAAA).
People use it to see how drinks, body weight and time interact. An 80 kg man who has had 3 standard drinks over 2 hours is estimated at 0.042 %, and the estimate reaches zero about 2 h 47 min later.
The result is an average-person model, not a measurement: food, drinking pace, medicines and liver function change real BAC, and impairment begins well below legal limits. It is not a basis for deciding whether to drive.
The Widmark formula spreads the alcohol you drank through a share r of body weight, 0.73 for men and 0.66 for women, then subtracts about 0.015 percentage points for every hour since the first drink. An 80 kg man who has had 3 US standard drinks over 2 hours is estimated at 0.042%.
It is an average-person estimate, not a measurement: never use it to decide whether to drive, operate machinery or look after others. Impairment starts below legal limits, and food, drinking pace, medicines and liver function all change real BAC.
In US units, BAC% = A × 5.14 ÷ (W × r) − 0.015 × H, where A is fluid ounces of pure alcohol, W is body weight in pounds and H is hours since the first drink. For the 80 kg man:
The 5.14 constant turns fluid ounces of alcohol and pounds of body weight into a percentage. It comes from 0.823 oz of weight per fluid ounce of ethanol × 100 ÷ 16 oz per pound.
NIAAA defines a US standard drink as 14 g, or 0.6 fl oz, of pure alcohol:
Many servings hold more than one. A 750 mL bottle of 12% wine contains 90 mL of alcohol, 71 g, or about 5 standard drinks. A UK pint (568 mL) of 5% beer holds 22.4 g, 1.6 standard drinks, and a US pint (473 mL) 18.7 g.
Other countries count differently: a UK unit is 8 g, so one US standard drink is 1.75 UK units. For drinks of different strengths, add the pure alcohol of each one.
At 0.015 percentage points an hour, the time from the first drink to zero is the starting estimate ÷ 0.015. A BAC of 0.08% takes about 5 hours 20 minutes to clear.
The 80 kg man's starting 0.0719% clears 4.79 hours after his first drink, so 2 hours 47 minutes after the 2-hour point. One standard drink takes about 1.3 hours for a 100 kg man and 2.8 hours for a 50 kg woman.
Coffee, water and sleep do not speed this up. The liver sets the pace, and individual rates differ from the 0.015 average.
The formula treats all the alcohol as absorbed at the first drink. It cannot show BAC still rising after drinking stops, which NIAAA warns can happen.
The r values of 0.73 and 0.66 are averages; the share of the body that holds alcohol varies between people of the same weight and sex.
BAC in percent is grams of alcohol per 100 mL of blood. Per mille (‰), or g/L, is ten times the percent figure, so 0.08% is 0.8‰.
The driving limit is 0.08% in every US state except Utah, which lowered it to 0.05% in 2018, and 0.04% for US commercial drivers. England, Wales and Northern Ireland use 80 mg per 100 mL (0.08%), and Scotland 50 mg (0.05%).
If someone is confused, vomiting, having seizures, breathing slowly or irregularly, or hard to wake, call emergency services. Do not wait for a calculated BAC or a zero time. A BAC above 0.30% is in the range NIAAA describes as life-threatening.
BAC figures are percentages and alcohol is in grams.
| Scenario | Estimated BAC now (%) | Before elimination (%) | Pure alcohol (g) |
|---|---|---|---|
| Default | 0.042 | 0.072 | 42.0 |
| Female wine example | 0.137 | 0.182 | 71.0 |
| Floored zero | 0.000 | 0.024 | 14.0 |
In the last row, 5 hours of elimination (0.075) exceed the 0.024 starting estimate, so the result stops at zero instead of going negative.
The caffeine half-life calculator models how caffeine falls after a dose, and the water intake calculator estimates daily fluid needs. Neither changes how fast alcohol clears.
Checked against: 1.8 × 5.14 / (180 × 0.73) − 0.015 × 2 = 0.04041; zero after 0.070411/0.015 − 2 h = 2.6941 h
Checked against: A = 750/29.5735295625 × 0.12 = 3.04326 fl oz; 3.04326 × 5.14 / (130 × 0.66) − 0.045 = 0.13731
Checked against: 0.6 × 5.14 / (176.37 lb × 0.73) = 0.02395 < 0.015 × 5, so the estimate is 0
Checked against: Definition: A = 0 gives BAC 0
In the US, a standard drink contains 14 g (0.6 fl oz) of pure alcohol: 12 fl oz of 5 % beer, 5 fl oz of 12 % wine or 1.5 fl oz of 40 % spirits, according to NIAAA. Other countries use different sizes; a UK unit is 8 g, so one US standard drink is 1.75 UK units. A 750 mL bottle of 12 % wine holds about 71 g of alcohol, roughly 5 US standard drinks.
With the Widmark formula. The alcohol drunk is divided by body weight times r, the share of the body that holds it (0.73 for men and 0.66 for women here), and about 0.015 percentage points are subtracted for each hour since drinking began. A 180 lb man who has 3 standard drinks (1.8 fl oz of alcohol) peaks at 1.8 × 5.14 ÷ (180 × 0.73) = 0.070 % and is estimated at 0.040 % two hours later.
At the average elimination rate of about 0.015 percentage points per hour, a BAC of 0.08 % takes roughly 5 hours 20 minutes to reach zero. One US standard drink takes about 1.3 hours to clear for a 100 kg man and 2.8 hours for a 50 kg woman by this estimate. Coffee, water and sleep do not speed elimination; the liver sets the pace, and individual rates vary.
0.08 % in every US state except Utah, which lowered its limit to 0.05 % in 2018, and 0.04 % for US commercial drivers. England, Wales and Northern Ireland use 80 mg per 100 mL of blood (0.08 %) and Scotland 50 mg (0.05 %). Impairment starts below these limits, so an estimate under the limit does not mean it is safe to drive.
For information only, not medical advice. These formulas describe populations, not you; talk to a clinician before acting on a result.
This calculator includes 5 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.