Blood Alcohol Concentration (BAC) Calculator
Pick your sex, enter your body weight, drinks consumed and hours since the first drink — the tool uses the classic 1932 Widmark formula to estimate your blood alcohol concentration (BAC, % w/v) and tells you how long until you fall below the Hong Kong 0.05% driving limit and until you are fully metabolised.
Please enter a valid number
Estimated BAC
0.029
% (g/100 mL)
Mild (< 0.03%)
—
Reference limits
0% HK driving limit
0.05% US driving limit
0.08% Severely intoxicated (0.15–0.30%)
0.15%+
Time until below the HK 0.05% driving limit
Already below the HK 0.05% driving limit
Time until fully eliminated (0%)
Already fully eliminated
The Widmark formula is only an approximation. Empty vs. full stomach, medication, health and ethnic alcohol-dehydrogenase variation all shift the result substantially. Never use this tool to decide whether to drive — don't drink and drive.
Formula
BAC % = (A × 100) / (W × r) − β × t A = grams of ethanol; W = body weight (g); r = 0.68 (M) / 0.55 (F); β = 0.015 %/h; t = hours elapsed
- · BAC is expressed in % w/v — grams of ethanol per 100 mL of blood. Hong Kong's Cap. 374 Road Traffic Ordinance sets the legal driver limit at 50 mg per 100 mL, i.e. 0.05%.
- · The definition of a "standard drink" varies: US 14 g, Hong Kong / WHO 10 g, UK 8 g (1 unit), Australia 12 g. Pick whichever matches the figures you've been counting.
- · Widmark r (body-water fraction) is the original 0.68 (M) / 0.55 (F). Women have a smaller distribution volume because of higher body-fat fraction, so the same dose yields a higher BAC.
- · The elimination rate β = 0.015 %/h is a literature average — the range is roughly 0.012–0.020. Habitual drinkers usually clear faster; light drinkers slower.
- · Drinking on an empty stomach, certain drugs (metronidazole, cefoperazone, disulfiram), liver function and the East-Asian ALDH2 variant can shift real BAC dramatically. The Widmark estimate and an actual breath / blood test can differ by tens of percent.
- · Sources: E. M. P. Widmark, 1932, Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung; NHTSA Driver Alcohol Detection System research; Hong Kong Cap. 374 Road Traffic Ordinance.
Frequently asked
What is the Hong Kong drink-driving limit and the penalty?
Under section 39A of Cap. 374, a driver commits an offence at 50 mg per 100 mL of blood (0.05% BAC), 22 μg per 100 mL of breath, or 67 mg per 100 mL of urine. A first conviction carries a fine up to HK$25,000, up to 3 years' imprisonment, a minimum 6-month disqualification, and a mandatory driving improvement course. Penalties escalate above 80 mg/100 mL or for repeat offences.
Is it OK to drive an hour after a single beer?
A 12 oz 5% beer is roughly 14 g of ethanol. For a 70 kg man one hour later this calculator estimates ≈ 0.015%, theoretically below the 0.05% limit. But Widmark assumes complete absorption — empty vs. full stomach changes the curve substantially, individual variation is large, and Hong Kong police breath-test on the spot. The estimate is no substitute for a real test. Don't drink and drive.
Does the "Asian flush" change my BAC?
The Asian flush is driven by the ALDH2*2 variant: acetaldehyde — the toxic intermediate — is metabolised slowly, accumulates and triggers vasodilation. BAC measures unmetabolised ethanol, not acetaldehyde, so BAC itself is not greatly inflated by the flush. However, accumulated acetaldehyde is an IARC Group 1 carcinogen and ALDH2*2 carriers have several-fold higher risks of oesophageal cancer and liver disease with chronic drinking. People who flush should drink especially sparingly.
Can coffee, a cold shower or exercise sober me up faster?
No. The rate at which BAC falls is set by hepatic alcohol-dehydrogenase metabolism and is essentially constant at about 0.015 %/h (≈ one drink per hour). Coffee makes you feel awake (caffeine blocks adenosine) but reaction time and judgement remain impaired; a cold shower might startle you but BAC is unchanged; exercise only dehydrates you further. The only remedy is time and water.
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