BAC Calculator

Methodology

BAC% = (drinks × 14 g) ÷ (weight in g × r) × 100 − 0.015 × hours. r is the Widmark factor, the share of body weight that alcohol spreads through: 0.68 for men and 0.55 for women. Pounds are converted at 453.59237 g. Hours count from the first drink, and the result never goes below 0. An estimate that would print as 0.000% is shown as “Estimate: 0.00%”. The estimate is shown to three decimals and labeled “Below 0.05%”, “0.05% to 0.079%: over the limit in Utah and in many countries” or “0.08% or more: over the US limit”. Those labels are for the US, the default. With Legal limit for set to Canada, England, Wales and Northern Ireland, or Scotland, the label says whether the estimate is at or over that place’s general limit (0.08%, 0.08% and 0.05%). Est. time to 0.00% = BAC ÷ 0.015 hours and Est. time to below the limit = (BAC − limit) ÷ 0.015 hours, both rounded to the nearest 5 minutes; a wait already passed shows as “None”, and a wait that rounds to 0 while the shown estimate is still at the limit shows as “Under 5 min”. A 160 lb man 1 hour after the first of 4 drinks is at 0.098%: 1 h 15 min to below 0.08% and 3 h 15 min to below 0.05%.

Assumptions

• Every drink is a US standard drink with 14 g of pure alcohol: 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits. A strong beer or a large pour counts as more than one.
• All the alcohol counts from the first drink. The formula does not model drinks spread over an evening or food in the stomach, which slows absorption.
• Elimination is fixed at 0.015% per hour. A review of measured rates found 0.010 to 0.015% per hour after drinking on an empty stomach, 0.015 to 0.020% after eating, and 0.025 to 0.035% in alcoholics during detoxification.
• The ratios 0.68 and 0.55 are averages. Women generally have less water per pound of body weight than men, which is why the same drinks give a higher figure.

Frequently asked questions

How many drinks does it take to reach 0.08?

By the Widmark formula, one hour after the first drink, a 180 lb man is at 0.086% after 4 standard drinks and a 150 lb woman is at 0.097% after 3. Lighter people get there on fewer drinks, as the tables show. NHTSA lists reduced coordination and difficulty steering at 0.05%, so the number of drinks that affects driving is lower than the number that reaches 0.08%.

How long does it take for BAC to go back to zero?

The calculator subtracts 0.015% per hour and shows the result as Est. time to 0.00%: an estimate of 0.076% gives 5 h 5 min, and 0.167% gives 11 h 5 min, with 5 h 45 min until it is below 0.08%. Measured elimination runs from about 0.010 to 0.035% per hour depending on the person, so the real time can be much longer or shorter. The hours table above shows the arithmetic: a 60 kg woman who had 4 drinks is still estimated at 0.050% 8 hours after the first. At zero the calculator prints “Estimate: 0.00%” and notes that alcohol can still be present. Do not use the estimate to plan a drive.

What is the legal BAC limit for driving?

In the US it is illegal to drive with a BAC of 0.08 g/dL or higher in every state except Utah, where the limit is 0.05. Lower limits apply to some drivers: 0.04 for commercial drivers on duty (49 CFR 382.201), and 0.02 or less for drivers under 21, the level federal law (23 U.S.C. 161) requires states to treat as driving under the influence. Being under the limit does not make driving safe: NHTSA counted 2,117 people killed in 2023 in crashes where a driver had a BAC of 0.01 to 0.07. In Canada the Criminal Code offence starts at 80 mg of alcohol in 100 mL of blood (s. 320.14), and some provinces add roadside suspensions at lower readings (Newfoundland and Labrador, for example, from 50 mg); England, Wales and Northern Ireland use 80 mg per 100 mL of blood and Scotland 50 mg since 5 December 2014. Pick the place under Legal limit for.

What counts as one standard drink?

In the US, 14 grams of pure alcohol, about 0.6 fluid ounces: a 12 oz can of 5% beer, a 5 oz glass of 12% wine or a 1.5 oz shot of 40% spirits. Enter 1.5 or 2 for a stronger or larger drink. The field accepts fractions.

Does spacing out my drinks change the estimate?

Not in this calculator. It counts every drink as taken at the moment of the first one and subtracts 0.015% for each hour since then, so three drinks at once and three spread over two hours both give a 180 lb man 0.046% two hours after the first. Food and slower drinking delay absorption, which the formula cannot see, so a measured BAC can differ in either direction.

What are the signs of alcohol poisoning?

NIAAA lists confusion or stupor, being hard to wake or unable to wake, vomiting, seizures, slow breathing (fewer than 8 breaths a minute), irregular breathing (10 seconds or more between breaths), slow heart rate, clammy skin, very low body temperature, and bluish or pale skin. Call 911 right away and do not wait for every sign.