Time to Sober Calculator

Blood Alcohol Content (BAC) clearance calculations estimate how long it takes for the liver to metabolize alcohol to zero. The liver works at a roughly constant rate, and nothing speeds it up. Not coffee, not food, not water, not a cold shower, not sleep. Time is the only variable.

BAC calculation formula (Widmark formula): BAC = (Alcohol Consumed in grams) ÷ (Body Weight in grams × Distribution Ratio) × 100

Where:

• Distribution Ratio (r): 0.68 for men, 0.55 for women (reflects different body water content)
• Alcohol in grams = Volume of drink (mL) × (ABV% ÷ 100) × 0.789 (density of ethanol)

That division by 100 matters. A 355 mL beer at 5% is 355 × 0.05 × 0.789 = 14 g, not 355 × 5 × 0.789.

Standard drink alcohol content:

• Beer (5%, 12 oz / 355 mL): ~14g alcohol
• Wine (12%, 5 oz / 148 mL): ~14g alcohol
• Spirit (40%, 1.5 oz / 44 mL): ~14g alcohol

All standard drinks contain approximately 14 grams of pure alcohol (US standard).

Metabolism rate: The liver eliminates alcohol at approximately 0.015–0.020% BAC per hour (the Widmark elimination constant β).

Time to sober up formula: Hours to Zero = BAC ÷ 0.015

The 0.015 figure is a population average, not a floor and not a guarantee. Individual elimination runs from about 0.010 to 0.020 per hour, so the honest answer to “when am I sober” is a range roughly 50% longer and 25% shorter than the single number, and this calculator shows both ends.

If you are a slow metaboliser and you plan around the average, you will be over the limit at the moment you believe you are clear. That is the failure mode worth designing against, so read the slow end of the range as the one that matters.

What each variable means:

• BAC 0.08%: the legal driving limit in the US (0.05% in most of Europe and Australia)
• r (distribution ratio): women have higher BAC per drink due to lower body water fraction and lower levels of alcohol dehydrogenase enzyme
• Food effect: food slows alcohol absorption but does NOT speed metabolism; it lowers peak BAC but doesn’t shorten clearance time

Reference: BAC effects

• 0.02–0.03%: Slight relaxation, mood lift
• 0.05–0.07%: Reduced inhibition, mild impairment
• 0.08%: Legal driving limit; coordination impaired
• 0.10–0.15%: Slurred speech, reaction time severely slowed
• 0.20%+: Severe impairment; blackout possible
• 0.30%+: Loss of consciousness; potentially fatal

Worked example: 170-lb man (77 kg) consumes 4 standard drinks over 2 hours.

Alcohol = 4 × 14g = 56g Body weight = 77 kg = 77,000 g Peak BAC = 56 ÷ (77,000 × 0.68) × 100 = 56 ÷ 52,360 × 100 = 0.107%

Metabolism over 2 hours = 2 × 0.015 = 0.030 BAC at end of drinking = 0.107 − 0.030 = 0.077%, just under the legal limit and still clearly impaired

Hours remaining to zero: 0.077 ÷ 0.015 = 5.1 additional hours at the average rate.

At the slow end of the range, 0.077 ÷ 0.010, it is 7.7 hours. That is the difference between being clear at 4 AM and being over the limit on the drive to work.