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Blood alcohol (BAC) calculator

Add what you drank and when. You get your estimated peak and current blood alcohol, plus how long until you are below your country's driving limit and back to 0.0 ‰ — at a typical and at a slow elimination rate.

Defaults to your region. Switch to compare any other scale.

Sex

Result

0.4 ‰ · 0.04 %

Blood alcohol at check time

Peak: 0.4 ‰ — reached at 23:00

  • Peak0.4 ‰ (23:00)
  • BAC (US / UK % notation)0.04 %
  • Below the limit (typical rate)now
  • Below the limit (slow rate)now
  • 0.0 ‰ (typical rate 0.15 ‰/h)in 2 h 40 min (at 01:40)
  • 0.0 ‰ (slow rate 0.10 ‰/h)in 5 h 30 min (at 04:30)
  • Pure alcohol48.1 g

Estimate is below the limit — still only an estimate

This is a statistical estimate, never a guarantee that you are sober or fit to drive. Real values vary by ±30 % or more with food, liver health, medication, fatigue and drinking speed. Alcohol impairs you even below the legal limit. If you have been drinking, do not drive — use a taxi, public transport or a sober driver.

Formula

  • Total body water (Watson 1980), men: TBW = 2.447 − 0.09516 × age + 0.1074 × height(cm) + 0.3362 × weight(kg)
  • Women: TBW = −2.097 + 0.1069 × height(cm) + 0.2466 × weight(kg)
  • Alcohol (g) = volume(ml) × ABV% ÷ 100 × 0.789
  • BAC (‰) = alcohol(g) × 0.8 ÷ TBW − β × hours; β typical 0.15 ‰/h (range 0.10–0.25)
  • BAC % = ‰ ÷ 10 (0.5 ‰ = 0.05 %)

How it is calculated

  1. Enter sex, age, weight and height.
  2. Add every drink and how many you had.
  3. Set when you started and how long you drank.
  4. Pick your country's limit and read when you drop below it and reach 0.0 ‰.

Questions

How long does it take for alcohol to leave the body?

The liver removes roughly 0.10–0.25 ‰ per hour, about 0.15 ‰ on average, and nothing (coffee, cold shower, sleep) speeds it up. From a 0.6 ‰ peak that is about 4 hours, and up to 6 hours for slow eliminators.

How many promille is 2 glasses of wine and a beer?

That is about 48 g of pure alcohol. For an 80 kg, 180 cm, 35-year-old man drinking over 2 hours the peak is roughly 0.4–0.6 ‰; a 60 kg woman reaches about 0.8–1.0 ‰.

Why does the calculator use the Watson formula?

Alcohol spreads in body water, not fat. Watson estimates total body water from sex, age, height and weight, so it is more accurate than the classic Widmark factor (0.68 / 0.55) for very lean or heavier people. Forensic labs often use it as the refined Widmark method.

Is it safe to drive once the calculator says I am under the limit?

No. It is an estimate with ±30 % uncertainty and only a breathalyser or blood test measures your real level. Impairment starts well below 0.5 ‰. Use the slow-rate time as a minimum, and when in doubt do not drive.

Sources

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