How is BAC calculated?

This calculator uses the Widmark formula: BAC% = (grams of alcohol ÷ (body weight in grams × r)) × 100 − (0.015 × hours). Grams of alcohol = standard drinks × 14. The Widmark factor r is 0.68 for men and 0.55 for women, reflecting average body-water fraction. The 0.015 term is the average hourly elimination rate.

What BAC is legally drunk in the US?

0.08% is the per-se legal driving limit in every US state except Utah, which lowered it to 0.05% in 2019. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance laws (0.00-0.02% depending on state). You can still be charged for impaired driving below 0.08% if an officer observes impairment.

How long does it take to sober up?

Your body clears alcohol at a roughly fixed rate of about 0.015% BAC per hour — there is no way to speed it up. From a BAC of 0.08%, that is roughly 5.3 hours to reach 0.00%. From 0.15%, it is about 10 hours. Coffee, cold showers, food, and water make you feel more alert but do not lower your actual BAC.

Does food or water lower your BAC?

Eating before or while drinking slows alcohol absorption, so your peak BAC is lower and arrives later — but once alcohol is in your blood, food does not remove it. Water reduces dehydration symptoms but does not dilute BAC. Nothing speeds elimination except time. The 'sober up fast' tricks are myths.

Why do women reach a higher BAC than men?

On average, women have a higher proportion of body fat and a lower proportion of body water than men of the same weight. Alcohol distributes into body water, so with less water to dilute it, the same number of drinks produces a higher concentration. That is why the Widmark factor is 0.55 for women versus 0.68 for men.

How many drinks does it take to reach 0.08%?

It depends heavily on weight, sex, and time. A 160 lb man reaches roughly 0.08% after about 4 standard drinks in 1 hour; a 120 lb woman can reach it after about 2-3 drinks. Drinking over a longer period lowers the result because elimination runs continuously. Use the calculator with your own numbers — these are only ballpark figures.

What does a BAC of 0.08% feel like?

At 0.08% most people show impaired muscle coordination, slower reaction time, reduced judgment, and harder-to-control speech and balance — the exact skills needed to drive. Impairment is measurable from as low as 0.02% (some loss of judgment and divided-attention ability). 'Feeling fine' is itself a symptom of impaired self-assessment.

Can I use this calculator to decide if I'm safe to drive?

No. The Widmark formula is a population estimate that can be off by 0.02% or more for any individual because of food, medications, body composition, liver health, drinking pace, and genetics. It is an educational tool, not a breathalyzer or a legal defence. The only safe blood alcohol level for driving is 0.00 — if you have been drinking, do not drive.

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BAC Calculator — Blood Alcohol Content by Drinks, Weight & Time

Estimate your blood alcohol content (BAC) from standard drinks, body weight, sex, and hours since your first drink — with impairment level, the 0.08% legal limit, and time-to-sober. Educational only: the only safe BAC to drive is 0.00.

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Reviewed by CalcBold Editorial · Sources: NIAAA + NHTSA + CDC (Widmark 1932)Last verified June 9, 2026Methodology

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Blood alcohol content (BAC) is the percentage of alcohol in your bloodstream. This calculator estimates it with the Widmark formula: grams of alcohol (standard drinks × 14) divided by your body-water mass (weight in grams × r), minus what your body has metabolized at about 0.015% per hour. The US legal driving limit is 0.08%, but impairment begins far lower — the only safe BAC to drive is 0.00.

The Widmark Formula — The Math

Estimated blood alcohol content

BAC% = (A / (W_g × r)) × 100 − (β × t)
A = standard_drinks × 14 g · W_g = weight in grams · r = 0.68 male / 0.55 female · β = 0.015 %/hr · t = hours

A is the grams of pure alcohol consumed (one US standard drink = 14 g). W_g is body weight in grams, and r is the Widmark distribution ratio — the fraction of your body that is water, which is where alcohol distributes. The β·t term subtracts what your liver has already metabolized at roughly 0.015% BAC per hour.

Source:NIAAA — What Is A Standard Drink?· National Institute on Alcohol Abuse and Alcoholism

What Counts As One Standard Drink

Mis-counting drinks is the single biggest source of error. One US standard drink contains 14 grams of pure alcohol, which works out to:

12 oz of regular beer (about 5% alcohol)
5 oz of wine (about 12% alcohol)
1.5 oz of distilled spirits (about 40% / 80 proof)

Real-world pours rarely match these. A pint of craft IPA at 7% is roughly 1.5 standard drinks; a generous restaurant wine pour can be 1.5–2; a margarita or long-island can be 2–3. When in doubt, count up, not down.

Why Time Is the Only Thing That Sobers You Up

Your liver metabolizes alcohol at a roughly fixed rate — about 0.015% of BAC per hour, regardless of what you do. That means from a BAC of 0.08% it takes about 5.3 hours to return to 0.00%, and from 0.15% it takes around 10 hours. Coffee, cold showers, water, exercise, and greasy food can make you feel more alert, but they remove zero alcohol from your blood. The “sober up fast” tricks are myths — only time works.

Impairment Begins Long Before 0.08%

The legal limit is where the law steps in, not where impairment starts. Measurable loss of judgment and divided-attention ability appears around 0.02%; by 0.05% most drivers show reduced coordination, slower tracking, and impaired response to emergencies. By 0.08% — the per-se limit in every US state except Utah (0.05%) — the specific skills driving requires are clearly degraded. Commercial drivers are held to 0.04%, and drivers under 21 face zero-tolerance laws.

Worked example

180 lb man, 4 standard drinks, 2 hours

Drinks: 4 standard
Weight: 180 lb (81.6 kg)
Sex: Male (r = 0.68)
Hours: 2

Grams of alcohol consumed.
4 × 14 = 56 g
Body-water mass = weight in grams × r.
81,647 × 0.68 ≈ 55,520 g
Peak BAC before metabolism.
(56 / 55,520) × 100 ≈ 0.101%
Subtract metabolism over 2 hours.
0.101 − (0.015 × 2) = 0.071%

Estimated BAC ≈ 0.071% — noticeable impairment, just under the 0.08% limit. It would take roughly 4h 45m to return to 0.00%.

Under the limit is NOT safe to drive — driving skills are measurably impaired at 0.07%. The only safe driving BAC is 0.00.

Why Women and Men Reach Different BACs

On average, women carry a higher proportion of body fat and a lower proportion of body water than men of the same weight. Because alcohol distributes into body water, less water means a higher concentration from the same number of drinks. That is why the Widmark factor is 0.55 for women and 0.68 for men. Other individual factors — liver health, medications, hormonal cycle, and genetic variants like ALDH2 — shift the real number further, which is why no formula can tell you it is safe to drive.

Recognizing Alcohol Poisoning

Very high BAC is a medical emergency, not just a bad night. Signs of alcohol poisoning include confusion, repeated vomiting, slow or irregular breathing (under 8 breaths per minute or 10+ seconds between breaths), pale or blue-tinged skin, low body temperature, and unconsciousness or inability to wake. If you see these signs, call 911 immediately, keep the person sitting up or on their side, and do not leave them to “sleep it off” — BAC can keep rising even after the last drink as alcohol in the stomach continues to absorb.

Pair It With

Drinking carries a money cost as well as a health one. The Alcohol Cost calculator shows the lifetime spend of your drinking pattern, and the Calorie / TDEE calculator puts the ~7 calories per gram of alcohol in context against your daily energy budget — a heavy night can quietly erase a week of calorie deficit.

Frequently Asked Questions

The most common questions we get about this calculator — each answer is kept under 60 words so you can scan.

How is BAC calculated?
This calculator uses the Widmark formula: BAC% = (grams of alcohol ÷ (body weight in grams × r)) × 100 − (0.015 × hours). Grams of alcohol = standard drinks × 14. The Widmark factor r is 0.68 for men and 0.55 for women, reflecting average body-water fraction. The 0.015 term is the average hourly elimination rate.
What BAC is legally drunk in the US?
0.08% is the per-se legal driving limit in every US state except Utah, which lowered it to 0.05% in 2019. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance laws (0.00-0.02% depending on state). You can still be charged for impaired driving below 0.08% if an officer observes impairment.
How long does it take to sober up?
Your body clears alcohol at a roughly fixed rate of about 0.015% BAC per hour — there is no way to speed it up. From a BAC of 0.08%, that is roughly 5.3 hours to reach 0.00%. From 0.15%, it is about 10 hours. Coffee, cold showers, food, and water make you feel more alert but do not lower your actual BAC.
Does food or water lower your BAC?
Eating before or while drinking slows alcohol absorption, so your peak BAC is lower and arrives later — but once alcohol is in your blood, food does not remove it. Water reduces dehydration symptoms but does not dilute BAC. Nothing speeds elimination except time. The 'sober up fast' tricks are myths.
Why do women reach a higher BAC than men?
On average, women have a higher proportion of body fat and a lower proportion of body water than men of the same weight. Alcohol distributes into body water, so with less water to dilute it, the same number of drinks produces a higher concentration. That is why the Widmark factor is 0.55 for women versus 0.68 for men.
How many drinks does it take to reach 0.08%?
It depends heavily on weight, sex, and time. A 160 lb man reaches roughly 0.08% after about 4 standard drinks in 1 hour; a 120 lb woman can reach it after about 2-3 drinks. Drinking over a longer period lowers the result because elimination runs continuously. Use the calculator with your own numbers — these are only ballpark figures.
What does a BAC of 0.08% feel like?
At 0.08% most people show impaired muscle coordination, slower reaction time, reduced judgment, and harder-to-control speech and balance — the exact skills needed to drive. Impairment is measurable from as low as 0.02% (some loss of judgment and divided-attention ability). 'Feeling fine' is itself a symptom of impaired self-assessment.
Can I use this calculator to decide if I'm safe to drive?
No. The Widmark formula is a population estimate that can be off by 0.02% or more for any individual because of food, medications, body composition, liver health, drinking pace, and genetics. It is an educational tool, not a breathalyzer or a legal defence. The only safe blood alcohol level for driving is 0.00 — if you have been drinking, do not drive.