BAC Calculator

How to Use This Calculator

Our BAC calculator uses the Widmark formula to estimate your blood alcohol concentration based on your gender, body weight, the number of standard drinks consumed, and the time elapsed since your first drink.

Steps:

1. Select your gender (male or female)
2. Enter your body weight in kilograms or pounds
3. Enter the total number of standard drinks you've consumed
4. Enter how many hours have passed since your first drink
5. View your estimated BAC, impairment level, and time to sober up

Important: This calculator provides estimates only. Actual BAC depends on many individual factors and can only be measured accurately with a breathalyzer or blood test. Never use this calculator to determine if you are legally safe to drive.

How BAC Is Calculated

The Widmark formula, developed by Swedish physician Erik Widmark in the 1920s, is the most widely used method for estimating blood alcohol concentration from known variables. The formula is:

BAC = (A × 5.14) / (W × r) - (0.015 × H)

Where:

• A = total alcohol consumed in ounces (1 standard drink = 0.6 oz of pure alcohol)
• W = body weight in pounds
• r = gender constant (0.73 for males, 0.66 for females)
• H = hours since the first drink
• 0.015 = average alcohol elimination rate per hour

The gender constant (r) reflects that men have, on average, a higher percentage of body water than women. Since alcohol distributes throughout body water, a man with the same weight and alcohol intake as a woman will generally have a lower BAC because the alcohol is more diluted.

The elimination rate of 0.015% per hour (about 1 standard drink per hour) is an average. Individual rates vary from about 0.01% to 0.02% per hour depending on genetics, liver function, and drinking history.

Standard Drink Sizes

A “standard drink” contains approximately 14 grams (0.6 ounces) of pure alcohol. However, what looks like “one drink” can vary enormously:

In practice, many drinks contain more alcohol than a standard drink. A pint of craft beer at 7% ABV is actually about 1.7 standard drinks. A generous pour of wine at a restaurant could easily be 7-8 oz, which is 1.5-2 standard drinks. Mixed drinks may contain 2-4 oz of spirits, making them 1.5-3 standard drinks each.

Standard drink sizes also vary by country. The UK standard drink (unit) contains 8 grams of alcohol, Australia's standard drink contains 10 grams, and Japan's standard unit contains about 20 grams. This calculator uses the US standard of 14 grams per drink.

How the Body Processes Alcohol

Unlike food, alcohol is not digested — it's absorbed directly into the bloodstream through the stomach and small intestine. About 20% is absorbed through the stomach walls, and the remaining 80% is absorbed through the small intestine.

Once in the bloodstream, alcohol travels to the liver, which is the primary organ responsible for metabolizing alcohol. The liver uses enzymes (primarily alcohol dehydrogenase) to break alcohol down into acetaldehyde, then into acetate, and finally into water and carbon dioxide.

The liver can process roughly one standard drink per hour, regardless of how much you drink. Drinking faster than the liver can process leads to alcohol accumulating in the bloodstream, raising your BAC. Nothing speeds up this process — not coffee, cold showers, exercise, or vomiting. Only time reduces BAC.

A small amount of alcohol (about 2-5%) is eliminated through breath, sweat, and urine, which is why breathalyzer tests work. But the vast majority is processed by the liver at its fixed rate.

Factors That Affect BAC

• Body weight: Heavier people have more blood volume, so the same amount of alcohol is more diluted, resulting in a lower BAC.
• Gender:Women generally have a higher proportion of body fat and lower body water than men of the same weight. Since alcohol is water-soluble (not fat-soluble), it becomes more concentrated in women's blood.
• Food intake: Drinking on an empty stomach leads to faster absorption and higher peak BAC. Eating a meal before or while drinking slows absorption significantly, particularly foods high in protein, fat, and complex carbohydrates.
• Drinking speed: The liver processes alcohol at a fixed rate. Drinking multiple drinks in a short period causes BAC to rise much faster than the same drinks consumed over several hours.
• Medications: Many medications interact with alcohol, including antibiotics, antidepressants, pain relievers, and antihistamines. Some slow alcohol metabolism, while others amplify its effects. Always check medication labels for alcohol interaction warnings.
• Tolerance:While regular drinkers may feel less impaired at a given BAC, their actual BAC is the same as a non-drinker's. Tolerance affects perceived impairment, not measured BAC.
• Age: As people age, their body water percentage tends to decrease and liver function may decline, both of which can lead to higher BAC from the same amount of alcohol.

Legal BAC Limits

Legal BAC limits for driving vary significantly by country and circumstance:

Many countries have lower limits for young drivers, commercial drivers, or novice license holders. In the US, all states have zero-tolerance laws for drivers under 21, meaning any detectable BAC is illegal.

When Is It Safe to Drive

The only safe BAC for driving is 0.00%. Even at BAC levels below the legal limit (0.02-0.05%), research shows measurable impairment in reaction time, tracking ability, and divided attention. The risk of a crash begins to increase significantly at 0.05%, even though this is legal in many countries.

Common myths about sobering up:

• Coffee does not lower BAC. It may make you feel more alert, but your reaction time and judgment remain impaired. A caffeinated drunk driver is still a drunk driver.
• Cold showers do not lower BAC. Shock and adrenaline may temporarily increase alertness, but they do not speed up alcohol metabolism.
• Exercise does not lower BAC. While you may sweat out a tiny amount of alcohol, the effect is negligible. Over 95% of alcohol is metabolized by the liver.
• Vomiting does not significantly lower BAC if the alcohol has already been absorbed into the bloodstream (which happens within 30-60 minutes for most drinks).
• Drinking water does not lower BAC. It helps with dehydration but does not accelerate alcohol metabolism.

If you've been drinking, the safest choices are: have a designated driver, use a rideshare service or taxi, take public transportation, or stay where you are. The cost of any of these is always less than a DUI.

Frequently Asked Questions

How accurate is the Widmark formula?

The Widmark formula provides a reasonable estimate for most people but has a typical margin of error of 0.01-0.02% compared to actual measured BAC. Individual factors like food intake, medications, genetics, and liver health can cause actual BAC to differ significantly from the estimate. Never rely on any formula or calculator to determine if it's safe to drive.

How long does it take to sober up?

The liver metabolizes alcohol at an average rate of 0.015% BAC per hour, which is roughly equivalent to one standard drink per hour. If your BAC is 0.12%, it would take approximately 8 hours to reach 0.00%. This rate varies between individuals from about 0.01% to 0.02% per hour, but it cannot be sped up by any method.

Can I get a DUI even if I feel fine?

Yes. BAC is an objective measurement, and you can be over the legal limit without feeling impaired. Tolerance to alcohol's subjective effects does not change your actual BAC or its impact on reaction time and judgment. Police can also arrest you for impaired driving even if your BAC is below the legal limit if they observe signs of impairment.

Does body fat percentage affect BAC?

Yes. Alcohol is water-soluble, not fat-soluble, so it distributes into body water. People with higher body fat percentages have less body water relative to their weight, meaning the same amount of alcohol becomes more concentrated in their blood, resulting in a higher BAC.

Why is the legal limit 0.08% in the US?

The federal government pushed all US states to adopt 0.08% as the legal BAC limit for driving in 2000, tying federal highway funding to compliance. Before this, most states had a 0.10% limit. Research has shown that crash risk doubles at 0.05% and increases dramatically at 0.08% and above. Many countries have since adopted lower limits (0.05% or less).

What is binge drinking?

The CDC defines binge drinking as consuming 5 or more drinks for men, or 4 or more drinks for women, within about 2 hours. This pattern typically raises BAC to 0.08% or above. Binge drinking is associated with a wide range of health risks including alcohol poisoning, accidents, liver disease, heart disease, and increased risk of certain cancers. It accounts for over half of all alcohol-related deaths in the US.