Blood Alcohol Calculator (Widmark): BAC and Time to Sober Up

When will I be sober? Widmark BAC and promille

This alcohol level calculator applies the Widmark formula with its original coefficients: peak blood alcohol = grams of alcohol ÷ (weight × 0.68 for a man or 0.55 for a woman), reached 30 min after the first drink on an empty stomach or 1 h with a meal, then a fixed drop of 0.12 g/L per hour. It plots the hour-by-hour curve and works out how long until you fall below the chosen limit: 0.50, 0.20 or 0.80 g/L. It also tells you when you will be sober as a clock time, converts a level between g/L, ‰, % BAC and mg/L of breath, and, as a prevention guide, shows the number of drinks beyond which a given level is probably exceeded.

The calculation

• Pure alcohol (g) = volume (ml) × ABV ÷ 100 × 0.8; one standard drink counts as 10 g.
• Peak (g/L) = pure alcohol ÷ (weight × r), with r = 0.68 (men) or 0.55 (women) and weight floored at 35 kg.
• Linear rise to the peak, then a fixed drop of 0.12 g/L per hour.
• Wait = (current level − limit) ÷ 0.12; before the peak, time left to the peak + (peak − limit) ÷ 0.12. Breath alcohol = level ÷ 2 (2,000:1 ratio).

Example

A 75 kg man has two 50 cl beers at 5% and a 12.5 cl glass of wine at 12.5% with a meal: 40 g + 12.5 g = 52.5 g, or 5.3 standard drinks. Peak: 52.5 ÷ (75 × 0.68) = 1.03 g/L at 1 h. Two hours after the first drink: 1.03 − 0.12 = 0.91 g/L (0.46 mg/L of breath). Wait before 0.50 g/L: 3 h 24; before 0.20 g/L: 5 h 54; before 0.80 g/L: 54 min; back to zero: 7 h 36.

When will I be sober? The clock time

The "Current time" field takes your device's clock and can be changed. The tool adds the computed waits to it: the top of the result shows when you are back to 0.00 g/L, then when you fall below 0.50 and 0.20 g/L, and recalls when the first drink was. With the example above and 22:00 as the current time, the first drink was at 20:00: below 0.50 g/L at 01:24, below 0.20 g/L at 03:54, sober at 05:36 the next day. These times use the waits rounded to a tenth of an hour.

Three waits side by side

Whatever limit you select, the tool also shows three waits: below 0.50 g/L (general limit in France), below 0.20 g/L (in France: probationary licence, learner drivers, public transport) and back to 0.00 g/L. Each follows the wait formula above, rounded to a tenth of an hour. Example: a 60 kg woman has three 25 cl beers at 5% on an empty stomach, i.e. 30 g of pure alcohol or 3 standard drinks. Peak: 30 ÷ (60 × 0.55) = 0.91 g/L at 30 min. Two hours after the first drink: 0.91 − 1.5 × 0.12 = 0.73 g/L. Below 0.50 g/L: (0.73 − 0.50) ÷ 0.12 = 1.9 h, i.e. 1 h 54; below 0.20 g/L: 4.4 h, i.e. 4 h 24; back to zero: 6.1 h, i.e. 6 h 06.

BAC to promille and breath alcohol conversions

The percentage used in the United States (BAC) refers to 100 mL of blood: 0.08% = 0.80 g/L. Promille is counted like g/L, as the legal limits do: 0.50 g/L or 0.25 mg/L of breath in France (art. R234-1), 0.5 ‰ or 0.25 mg/L in Germany (§ 24a StVG), 0.5 g/L or 0.25 mg/L in Spain (art. 20 of the Reglamento General de Circulación). These three countries therefore use a 2,000:1 blood/breath ratio, i.e. mg/L = g/L ÷ 2. US federal rules measure breath alcohol in grams per 210 litres (49 CFR § 40.3), a 2,100:1 ratio: there 0.08% matches 0.381 mg/L. The tool shows the ratio used under the result. Example: 0.12% BAC = 1.20 g/L = 1.20 ‰ = 0.600 mg/L (2,000:1) or 0.571 mg/L (2,100:1). At an alcohol dissipation rate of 0.12 g/L (0.012% BAC) per hour, a .12 BAC gets back to zero in 10 h; at 0.15 to 0.10 g/L per hour, in 8 to 12 h. The other way round, 0.25 mg/L of breath = 0.50 g/L = 0.050%.

How many drinks to reach a given BAC?

The reverse mode starts from the level entered in the converter and reuses the sex, weight, meal and time since the first drink: alcohol (g) = (level + 0.12 × hours elapsed after the peak) × weight × r, divided by the size of a standard drink. That size depends on the country: 10 g in France (French road safety) and Spain (UBE, Spanish Ministry of Health, 2022), 14 g in the United States (NIAAA), 8 g per unit in the United Kingdom (NHS). Reaching the limit is already an offence, so the tool gives the number of drinks beyond which the level is probably exceeded. Example: for a 75 kg man with a meal, 2 h after the first drink, 0.50 g/L (BAC 0.05) matches 3.1 drinks of 10 g (beyond 3 drinks) or 2.2 US drinks of 14 g (beyond 2 drinks). 3 drinks in 2 hours, with US drinks of 14 g (42 g), give a BAC of 0.70 g/L (0.070%) for this man and 1.09 g/L (0.109%) for a 60 kg woman on an empty stomach. This is a prevention guide, not a target: the only safe BAC for driving is zero, and the Widmark formula remains an estimate.

Limits

All drinks count as taken with the first one. Before the peak, the verdict is based on the peak still to come: at 0 h the level shown is 0.00 g/L, but the tool says not to drive and announces a 5 h 24 wait, i.e. 1 h of rise to 1.03 g/L, then the fall to 0.50 g/L. Reaching the limit itself is an offence (French art. R234-1): you have to be below it. The 0.12 g/L/h rate is fixed, while French road safety gives 0.10 to 0.15 g/L/h. The result is indicative: a breathalyser and medical advice have the final word.

Sources and dates: French Highway Code, art. R234-1 (in force since 24/08/2019): 0.50 g/L, or 0.20 g/L for novice drivers; GOV.UK, "The drink drive limit": 80 mg/100 ml (0.80 g/L) in England, Wales and Northern Ireland, 50 mg in Scotland; NHTSA, "Lower BAC Limits": 0.08 g/dL in every state except Utah, at 0.05 g/dL since 30/12/2018; French road safety alcohol leaflet, April 2022: 0.10 to 0.15 g/L/h, 10 g per drink. NIAAA, "What Is A Standard Drink?" (updated December 2025): 14 g; NHS, "Calculating alcohol units" (reviewed 27/08/2024): 1 unit = 10 ml or 8 g; Spanish Ministry of Health (2022): 1 UBE = 10 g; 49 CFR § 40.3: grams of alcohol per 210 L of breath; § 24a StVG: 0.5 ‰ or 0.25 mg/L; Reglamento General de Circulación, art. 20: 0.5 g/L or 0.25 mg/L. Widmark (1932) (checked 14/10/2026, additions checked 22/10/2026).

Frequently Asked Questions

What is the Widmark formula?

Proposed by Swedish chemist Erik Widmark in 1932, it estimates blood alcohol by dividing the mass of alcohol consumed by body weight times a distribution factor r (0.68 for men, 0.55 for women in this tool). An hourly elimination is then subtracted, here 0.12 g/L. For 52.5 g of alcohol, a 75 kg man peaks at 1.03 g/L.

When will I be sober?

The tool adds the wait until 0.00 g/L to the current time, taken from your device and editable. It shows that clock time at the top of the result, along with the times you fall below 0.50 and 0.20 g/L. A 75 kg man who had two 50 cl beers and a glass of wine with a meal, starting at 20:00, gets below 0.50 g/L at 01:24 and below 0.20 g/L at 03:54, then back to zero at 05:36. These are estimates: if in any doubt, do not drive.

How many drinks to reach 0.5 g/L (BAC 0.05% or 0.25 mg/L)?

Taken at once, a 10 g standard drink adds about 0.20 g/L to the peak of a 75 kg man and 0.30 g/L for a 60 kg woman. The 0.50 g/L level, i.e. 0.25 mg/L of breath or a BAC of 0.05%, matches 2.5 drinks for him and 1.6 for her: beyond 2 drinks for him and 1 drink for her, it is probably exceeded. For 0.20 g/L, it is beyond 1 drink for him and from the first drink for her. With US standard drinks of 14 g, the man goes over 0.05% beyond 1 drink. This is a prevention guide: the only safe BAC for driving is zero.

How do I convert BAC to promille or to breath mg/L?

BAC in % refers to 100 ml of blood: multiply it by 10 to get g/L, which count as promille (0.08% = 0.80 g/L = 0.8 ‰). For breath alcohol, divide g/L by 2 in France, Spain and Germany (0.50 g/L = 0.25 mg/L); in the United States, the 2,100:1 ratio makes 0.08% match 0.381 mg/L. 0.08% is the limit in England, Wales and Northern Ireland (80 mg per 100 ml, 50 mg in Scotland) and in every US state except Utah (0.05%). In France, 0.80 g/L is where a fine turns into a criminal offence.

How much alcohol is in a standard drink?

It depends on the country: about 10 g of pure alcohol in France according to French road safety, 10 g in Spain (UBE), 14 g in the United States according to the NIAAA and 8 g per unit in the United Kingdom according to the NHS. In France, a 25 cl beer at 5%, a 10 cl glass of wine at 12% or 3 cl of whisky at 40% each hold roughly 10 g, and a 50 cl beer at 5% holds 20 g. The tool's "how many drinks" mode offers these three sizes.

Why does the simulator say not to drive when my current level is low?

Right after drinking, the level keeps rising until the peak, 30 min later on an empty stomach or 1 h with a meal. Before that peak, the tool therefore judges the peak still to come. With two 50 cl beers and a glass of wine it shows 0.00 g/L at 0 h but says not to drive, because the level will reach 1.03 g/L an hour later; the wait before 0.50 g/L is 5 h 24.

How long does it take to get below 0.5 g/L?

First the level reaches its peak, 30 min after the first drink on an empty stomach or 1 h with a meal; then count (peak − 0.50) ÷ 0.12 hours, as the tool uses a drop of 0.12 g/L per hour. A 60 kg woman who has three 25 cl beers on an empty stomach (30 g of alcohol) peaks at 0.91 g/L: she gets below 0.50 g/L about 3 h 54 after the first drink, below 0.20 g/L after 6 h 24 and back to zero after 8 h 06. These are estimates: if in any doubt, do not drive.

How long does it take to eliminate one drink, or a .12 BAC?

A standard drink of 10 g of alcohol raises the level by about 0.20 g/L for a 75 kg man and 0.30 g/L for a 60 kg woman. At 0.12 g/L per hour, eliminating it therefore takes about 1 h 40 for him and 2 h 30 for her, counted from the peak. A BAC of 0.12%, i.e. 1.2 g/L, gets back to zero in 10 h at that rate. French road safety gives 0.10 to 0.15 g/L per hour depending on the person, i.e. 8 to 12 h for 1.2 g/L; neither coffee nor a shower speeds this up.

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