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Blood Alcohol Calculator

Estimate blood alcohol content from drinks, weight, sex and elapsed time, with China legal thresholds.

The question of whether last night has worn off is where the trouble starts — a morning-after reading catches people every year, because alcohol is metabolised far more slowly than it feels. Enter weight, sex and what was drunk to estimate the current blood alcohol concentration, along with the peak and the time to complete metabolism, so that "is a night's sleep enough" gets at least an order of magnitude.

The statement that matters: this is an estimate — individual metabolism varies by two to three times, and food, the type of drink and general condition all move the real figure. The thresholds displayed follow the Chinese legal limits, so a driver elsewhere should check the local figure. And a result must never be used to decide whether to drive: after drinking, nobody should drive, and morning-after cases are not rare.

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How to use

  1. Enter weight, sex and the drinks consumed.
  2. Read the estimated concentration and the peak.
  3. Check the time to full metabolism.
  4. Treat the result as education only — never as clearance to drive.

How it works

How to enter data

Enter the amount drunk (mL) and the alcohol content (%vol) — e.g. 500 mL of beer is 500 and 4; about 100 mL of baijiu at 42% is 100 and 42.

How alcohol metabolism is computed

Pick your sex and enter weight and the hours since drinking (alcohol metabolizes at about 0.15 g/L per hour).

How to read the result

The result is an estimate: a BAC of 0.2 g/L or more already meets the drinking-driving standard — "one drink is fine" is an illusion, and overnight alcohol can also be drunk driving.

Calculation basis: the thresholds in China's GB 19522-2010 for drivers — a blood alcohol content of 20 mg/100 mL or more is drink driving and 80 mg/100 mL or more is drunk driving. In practice only the result of an official breath or blood test counts.

Code example

JavaScript Estimating with the Widmark formula 

function bac({ volumeMl, abv, weightKg, male, hours }) {
  const alcoholG = volumeMl * (abv / 100) * 0.789;   // density of ethanol
  const r = male ? 0.68 : 0.55;                      // body-water distribution factor
  const burn = male ? 0.015 : 0.017;                 // g/L metabolised per hour
  const raw = alcoholG / (weightKg * r) - burn * hours;
  return Math.max(0, raw);                           // g/L
}

// Two beers (1000mL at 4%), a 70kg man, three hours later ≈ 0.1 g/L
// An estimate only — never drive after drinking

Python The same formula in Python 

def bac(volume_ml, abv, weight_kg, male, hours):
    alcohol_g = volume_ml * (abv / 100) * 0.789
    r = 0.68 if male else 0.55
    burn = 0.015 if male else 0.017
    return max(0, alcohol_g / (weight_kg * r) - burn * hours)

# Chinese standard: >=0.2 g/L is drink-driving, >=0.8 g/L is drunk driving
# Individual variation is large; an estimate is no substitute for judgement — never drink and drive

FAQ

How much reaches the drunk-driving line?

For a 70 kg man: one 500 mL beer at 4% (about 15.8 g alcohol) peaks at a BAC of about 0.33 g/L, already above the 0.2 line; full metabolism takes about 2.2 hours. Lighter weight and higher alcohol content push the level up significantly.

Why do men and women differ?

Alcohol distributes in body fluids, and women have a lower fluid fraction than men (Widmark factor 0.55 for women, 0.68 for men), so for the same intake women have a higher BAC and slower metabolism. This tool applies the factor by sex automatically.

Does overnight alcohol count as drunk driving?

Yes. How long the BAC takes to fall below 0.2 g/L depends on intake and individual metabolism, and after heavy drinking it may still read as drunk driving the next morning. This tool's "X hours to drop below 0.2" is a reminder: trade time for safety, not feeling.

How is blood alcohol concentration estimated?

Using the Widmark formula: BAC = alcohol (g) / (weight kg x distribution factor r) - metabolic rate x time. Men's r is about 0.68 and women's 0.55, with a metabolic rate of about 0.1-0.15 g/L per hour. The result is an estimate with wide individual variation.

What are the drunk-driving and drunk standards?

China's standard: a blood alcohol content of 20 mg/100 mL (0.2 g/L) or more is drinking and driving; 80 mg/100 mL (0.8 g/L) or more is drunk driving. The former brings points and license suspension, the latter may constitute the crime of dangerous driving and criminal liability.

Do tea, coffee or cold water sober you up fast?

No. Caffeine and cold water only make you feel alert; the blood alcohol concentration doesn't drop, and metabolism is essentially set by the liver at about 0.1-0.15 g/L per hour. The only reliable options are waiting or a designated driver.

Roughly what does one beer read?

A 500 mL beer at 4.5% contains about 18 g of pure alcohol. A 60 kg man's theoretical peak is about 0.44 g/L, already above the 0.2 line; women, with a smaller factor, read higher. The actual result also depends on drinking speed and whether you're on an empty stomach.

Are the amount and weight recorded?

No. Weight, drinking amount and time are used only locally with the Widmark formula, not uploaded, stored, or connected to any law-enforcement or health system. A reminder: this tool is an estimate only and can't decide whether you can drive — actual testing and the law prevail.