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Alcohol Metabolism Calculator: When Can I Drive?

Estimate your blood alcohol concentration (BAC) curve with the Widmark formula. Enter gender, weight, drink type and volume to see when you can legally drive under China's 20/80 mg/100ml limits.

Overview

Estimate your blood alcohol concentration (BAC) curve over time using the Widmark formula and a 0.15 g/L/h ethanol elimination rate. Based on your gender, weight, drink type and volume, the tool reports when BAC drops below the 20 mg/100ml legal limit (drunk-driving line) and 80 mg/100ml severe-drunk line under Chinese law. All math runs locally in your browser. Results are estimates only — individual variance is large, and never drink and drive.

How to use

  1. Select gender (males and females have different body water coefficients r).
  2. Enter body weight in kg (range 30-200).
  3. Pick a drink type (baijiu/beer/wine/spirits/custom). A typical ABV auto-fills and can be edited.
  4. Enter the volume consumed (ml) and how long you spent drinking (linear absorption phase).
  5. Tick "empty stomach" to set absorption peak at 0.5h (otherwise 1h).
  6. Enter hours since you started drinking to see the current BAC and remaining time to drive.

Formula

Pure ethanol(g) = volume(ml) × ABV% × 0.789 (ethanol density g/ml). Peak BAC(g/L) = pure_ethanol / (weight_kg × r), where r = 0.68 (male) / 0.55 (female). BAC decays as peak − β × t with β = 0.15 g/L/h. BAC(mg/100ml) = BAC(g/L) × 100. China legal limits: ≥20 mg/100ml drunk-driving, ≥80 mg/100ml severe.

Common scenarios

70kg male drinks 100ml of 53% baijiu

Roughly 41.8g of pure ethanol. Peak BAC ≈ 87.9 mg/100ml (severe-drunk territory). About 4.5h to drop below 20 mg/100ml, ~6h to fully metabolize.

60kg female drinks one 500ml beer (5%)

About 19.7g pure ethanol. Peak BAC ≈ 59.7 mg/100ml (over the legal limit but below severe). About 2.5h before driving is legal, ~4h to fully metabolize.

80kg male sips 500ml of wine over 2 hours after dinner

About 47.3g pure ethanol. With non-empty stomach the BAC peak shifts later in the absorption phase. Around 5.5-6h before legally driving.

FAQ

How long after 500ml of 53% baijiu can I drive?

For a 70kg male, this means about 209g of pure ethanol with peak BAC around 440 mg/100ml (far above the severe-drunk line). It would take 30+ hours for BAC to drop below 20. Do not attempt; never drive.

Does drinking one 500ml 5% beer push BAC above 20 mg/100ml?

For a 60-70kg adult, BAC briefly exceeds 20 mg/100ml with a peak around 50-60 mg/100ml, usually not reaching the 80 severe line. Wait at least 1.5-2 hours after one beer and verify with this tool.

Is the Widmark formula accurate? How big is individual variance?

Widmark is a classic forensic-toxicology model with typical error around ±20%. Individual variance comes from liver enzyme activity, food intake and health status. Use the result for decision support only; never substitute it for an actual breathalyzer reading.

What are China's drunk-driving and severe-drunk thresholds? Penalties?

Per GB 19522-2010: BAC ≥ 20 mg/100ml is drunk driving (driver's license suspended 6 months, fine 1000-2000 yuan). BAC ≥ 80 mg/100ml is severe drunk driving (license revoked, criminal liability, 5-year ban on retesting).

Why does drinking on an empty stomach hit peak BAC faster?

On an empty stomach, gastric emptying is faster, accelerating absorption in the small intestine and producing peak BAC within 0.5h. With food (especially protein and fat), gastric emptying delays peak BAC to 1h or later. The total metabolized amount is unchanged.

Can BAC still be detected the next morning? Does carry-over drinking trigger a DUI?

Yes — heavy drinking can keep BAC above 20 mg/100ml well into the next morning. For example, finishing 500ml of baijiu at 22:00 may still leave detectable alcohol at 08:00 the next day. After heavy drinking, don't drive the morning after; self-test with a breathalyzer first.

Do strong tea, coffee or exercise speed up alcohol metabolism?

No. Ethanol is metabolized primarily by the liver at a roughly constant rate (β ≈ 0.15 g/L/h) in healthy adults. Caffeine from tea or coffee may make you feel alert but does not lower actual BAC. Sweat releases negligible amounts. The only effective approach is waiting.

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