Can I trust the number to decide whether to drive?

No, never. Widmark is a 100-year-old formula giving a rough average; reality varies by 25–40% depending on food intake, medications, hydration, sleep, body composition (fat contributes nothing to alcohol distribution volume) and genetic differences in alcohol dehydrogenase. Police measure blood or breath with certified devices. After drinking, the only safe rule is: don’t drive. Wait until the next day or use a taxi/public transport.

What is 1 "unit" of alcohol?

In Norwegian context, 1 unit is ~12 g pure alcohol, equivalent to a 0.33 L beer (4.7%), small wine glass (12 cl, 12%), or a drink (4 cl spirits, 40%). There is no international standard: UK uses 8 g/unit, US 14 g/drink, Japan 20 g/unit. Always check what the system means by "unit" before comparing numbers.

Why is the Norwegian limit 0.2?

Norway lowered the limit from 0.5 to 0.2 in 2001 based on research showing measurably reduced reaction time and risk judgement already at 0.2. Sweden has the same limit. Denmark, Germany, Netherlands: 0.5. UK, USA: 0.8. Hungary and some eastern European countries: 0.0 (zero tolerance). New drivers have a lower limit in many countries.

How much does BAC drop per hour?

Common rule: 0.10–0.20 per mille per hour, average 0.15. So 1.0 per mille takes ~7 hours to clear. Women metabolise slightly faster per kg but also peak higher, so net time is similar. Coffee, cold showers, food and exercise do NOT change metabolism (only how you feel), only time works.

Blood Alcohol (BAC) Calculator (Widmark)

Estimated BAC (per mille)

How it works

A rough estimate of blood alcohol based on the Widmark formula: per mille = grams of alcohol / (r × body weight) − elimination × hours, where r is 0.68 for men and 0.55 for women, and the body eliminates about 0.15 per mille per hour. The drink-driving limit in Norway is 0.2.

Important: this is only a rough estimate and varies greatly from person to person. Never use it to decide whether you can drive. After drinking, the safest choice is to leave the car.

About this tool

The BAC calculator gives a rough estimate of blood alcohol level after drinking, based on the Widmark formula: grams of alcohol / (r × body weight) - 0.15 × hours, where r is 0.68 for men and 0.55 for women. Enter sex, weight, number of alcohol units and hours since the first unit. Useful for understanding how alcohol affects you and how long until you’re sober. Never use the result to decide whether you can drive; individual variation is large.

How to use it

Choose sex and enter body weight in kg.
Enter the number of alcohol units (1 unit ≈ 12 g pure alcohol).
Enter hours since the first unit.
See the estimated BAC update live.

Examples

Man 80 kg, 3 beers in 2 hours

InputMale, 80 kg, 3 units, 2 hours

Output~0.36 per mille (well over the 0.2 limit)

Woman 65 kg, 2 wine glasses in 3 hours

InputFemale, 65 kg, 2 units, 3 hours

Output~0.22 per mille (still over 0.2)

For the same number of units, women reach higher BAC than men because body water content and distribution volume are smaller. Not a stereotype, pure physiology.

Common use cases

Understanding how long it takes to sober up after a party.
Setting responsible limits before a party or night out.
Illustrating the effect of weight, sex and pace on intoxication.
Teaching about alcohol and traffic in school or youth clubs.
Comparing when it’s safe to drive again after one, two or three units.

Frequently asked questions

Can I trust the number to decide whether to drive?: No, never. Widmark is a 100-year-old formula giving a rough average; reality varies by 25–40% depending on food intake, medications, hydration, sleep, body composition (fat contributes nothing to alcohol distribution volume) and genetic differences in alcohol dehydrogenase. Police measure blood or breath with certified devices. After drinking, the only safe rule is: don’t drive. Wait until the next day or use a taxi/public transport.
What is 1 "unit" of alcohol?: In Norwegian context, 1 unit is ~12 g pure alcohol, equivalent to a 0.33 L beer (4.7%), small wine glass (12 cl, 12%), or a drink (4 cl spirits, 40%). There is no international standard: UK uses 8 g/unit, US 14 g/drink, Japan 20 g/unit. Always check what the system means by "unit" before comparing numbers.
Why is the Norwegian limit 0.2?: Norway lowered the limit from 0.5 to 0.2 in 2001 based on research showing measurably reduced reaction time and risk judgement already at 0.2. Sweden has the same limit. Denmark, Germany, Netherlands: 0.5. UK, USA: 0.8. Hungary and some eastern European countries: 0.0 (zero tolerance). New drivers have a lower limit in many countries.
How much does BAC drop per hour?: Common rule: 0.10–0.20 per mille per hour, average 0.15. So 1.0 per mille takes ~7 hours to clear. Women metabolise slightly faster per kg but also peak higher, so net time is similar. Coffee, cold showers, food and exercise do NOT change metabolism (only how you feel), only time works.

Technical background

Widmark formula (Erik Widmark, 1932): BAC = A / (r · W) - β · t, where A = alcohol in grams, r = distribution coefficient (0.68 for men, 0.55 for women, average values), W = body weight in kg, β = elimination rate (0.15 per mille/hour, range 0.10–0.20 individually), t = time since intake in hours. Alcohol is assumed distributed in body water; r reflects the water-to-weight ratio. The model assumes full absorption (which takes 30–90 min depending on food), linear elimination (not quite true at low levels), and average sex values (individual variation 25–40%). Better models (Watson, Forrest, NHTSA) include age, height, hydration and body-fat percentage. All computation is local; no data sent. Never use this or any BAC model as legal or safety basis; real measurements need a calibrated breath or blood test.