BAC Calculator - Free Online Tool

Estimate your blood alcohol content based on drinks, body weight, and time elapsed

Welcome to our free Blood Alcohol Content (BAC) Calculator, a comprehensive tool that estimates your current BAC level using the scientifically established Widmark formula. Whether you are planning a night out, studying the effects of alcohol for educational purposes, or simply curious about how your body processes alcohol, this calculator provides detailed estimates to help you make informed decisions about your health and safety. Blood Alcohol Content, or BAC, is a measurement of the amount of alcohol present in your bloodstream, expressed as a percentage by weight. For example, a BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. This metric is the standard used by law enforcement agencies worldwide to determine legal intoxication for driving and other activities. Even small amounts of alcohol can affect your coordination, judgment, and reaction time, which is why understanding your BAC matters. When you consume an alcoholic beverage, the alcohol is absorbed into your bloodstream primarily through the stomach lining and small intestine. Absorption begins within minutes and typically peaks between 30 and 90 minutes after your last drink, depending on several factors. Once in the blood, alcohol is distributed throughout your body's water content, which is why body weight and composition significantly affect your BAC. Your liver then metabolizes the alcohol at a relatively constant rate, typically eliminating about 0.015% BAC per hour, though this rate varies between individuals. Our calculator uses the Widmark formula, the most widely accepted method for estimating BAC. Developed by Swedish physician Erik Widmark in the 1930s, this formula accounts for the total amount of alcohol consumed, your body weight, a gender-based distribution constant (known as the Widmark factor or r-value), and the time elapsed since your first drink. The formula is: BAC = (alcohol consumed in grams / (body weight in grams multiplied by the Widmark factor)) minus (metabolism rate multiplied by hours elapsed). The Widmark factor reflects the difference in body water content between males (typically 0.68) and females (typically 0.55), since alcohol distributes primarily through body water. Legal BAC limits vary significantly around the world. In the United States, the legal limit for driving is 0.08% for adults aged 21 and over, with stricter limits of 0.04% for commercial drivers and zero-tolerance policies (0.00% to 0.02%) for drivers under 21. The United Kingdom and Canada also set their limits at 0.08%, while Australia and Germany enforce a lower limit of 0.05%. Japan uses 0.03%, and Sweden has one of the strictest limits at 0.02%. Understanding the legal limit in your jurisdiction is essential, but it is equally important to recognize that impairment begins well before reaching any legal threshold. Several factors influence how quickly your BAC rises and how high it reaches. Gender plays a significant role: women generally reach higher BAC levels than men of the same weight after consuming the same amount of alcohol, due to differences in body water content, body fat percentage, and the enzyme alcohol dehydrogenase. Body weight matters because alcohol is distributed across body mass, so a heavier person will typically have a lower BAC from the same number of drinks. Food in your stomach dramatically affects absorption rate. Drinking on an empty stomach can result in a peak BAC up to twice as high as drinking after a full meal, because food slows the passage of alcohol into the small intestine where most absorption occurs. Your individual metabolism rate, hydration level, medications, and overall liver health also contribute to how your body handles alcohol. A standard drink in the United States contains approximately 14 grams of pure alcohol. This is equivalent to 12 ounces (355 ml) of regular beer at 5% ABV, 5 ounces (148 ml) of wine at 12% ABV, or 1.5 ounces (44 ml) of distilled spirits at 40% ABV. Many people underestimate how much they drink because actual servings often exceed these standard amounts. A pint of craft beer at 7% ABV, a generous pour of wine, or a strong cocktail may contain significantly more alcohol than one standard drink. This calculator goes beyond a simple BAC estimate. It provides a detailed impairment effects table showing how different BAC levels affect your body and mind, from subtle mood changes at 0.02% to life-threatening respiratory depression above 0.30%. You can add multiple drink types with custom sizes and alcohol percentages, adjust for food intake, select your country's legal limit for comparison, and view a visual timeline of how your BAC is projected to decline over time. All calculations are performed entirely in your browser, ensuring your privacy. Please remember that this calculator provides estimates based on population-level averages. Individual results can vary significantly based on genetics, tolerance, health conditions, medications, and other factors. Never use any BAC calculator as the sole basis for deciding whether it is safe to drive or operate machinery. When in doubt, always err on the side of caution and arrange alternative transportation.

Understanding Blood Alcohol Content

Blood Alcohol Content (BAC) measures the concentration of alcohol in your bloodstream as a percentage. It is the standard metric used by medical professionals and law enforcement to quantify intoxication and assess impairment levels.

How Blood Alcohol Content Works

When you drink alcohol, it passes through your stomach and into the small intestine, where the majority of absorption occurs. From there, alcohol enters the bloodstream and is distributed throughout your body's water-containing tissues. Your brain is particularly affected because it has a rich blood supply. Absorption typically peaks 30 to 90 minutes after your last drink, though this varies based on stomach contents and drink type. Once absorbed, your liver begins breaking down the alcohol using enzymes, primarily alcohol dehydrogenase and aldehyde dehydrogenase. The liver can only process a fixed amount of alcohol per hour, which is why BAC rises when you drink faster than your body can metabolize. The average person eliminates about 0.015% BAC per hour, though this ranges from 0.010% to 0.020% depending on individual factors.

The Widmark Formula

The Widmark formula, developed by Swedish physician Erik Widmark in the 1930s, remains the most widely used method for estimating BAC. The formula calculates BAC based on the total grams of alcohol consumed, body weight, a gender-specific distribution constant (the Widmark factor), and time elapsed since drinking began. The Widmark factor accounts for differences in body water content: males average approximately 0.68 and females approximately 0.55, reflecting the fact that women generally have a higher proportion of body fat (which does not absorb alcohol) relative to body water. While the formula provides reliable estimates for most people, its accuracy decreases at extreme body weights, with certain medical conditions, or when combined with medications that affect alcohol metabolism. The formula assumes linear elimination, which holds true for moderate consumption but may underestimate BAC at very high intake levels.

Factors That Affect Your BAC

Multiple factors determine how alcohol affects you. Gender is significant because women typically have less body water and more body fat than men of equal weight, leading to higher BAC from the same intake. Body weight matters because a larger body has more water volume to dilute the alcohol. Food is perhaps the most controllable factor: eating a substantial meal before or while drinking can reduce peak BAC by up to 50% compared to drinking on an empty stomach, because food slows gastric emptying and delays absorption. Your individual metabolism rate depends on liver enzyme activity, which is influenced by genetics, age, regular alcohol consumption patterns, and overall liver health. Medications such as aspirin, H2 blockers, and certain antibiotics can interact with alcohol metabolism. Carbonated drinks may accelerate absorption, while the type of alcohol (beer vs. spirits) matters less than the total amount of pure alcohol consumed.

Legal Limits and Safety

Legal BAC limits for driving vary by country: 0.08% in the US, UK, and Canada; 0.05% in Australia and Germany; 0.03% in Japan; and 0.02% in Sweden. However, impairment begins well below these thresholds. Studies show that at just 0.02% BAC, drivers experience reduced visual function and difficulty performing two tasks simultaneously. At 0.05%, steering control and emergency response are noticeably degraded. The legal limit is not a safe limit — it is the point at which penalties are enforced. Many alcohol-related accidents involve drivers with BAC levels below the legal limit. The only truly safe BAC for driving is 0.00%. This calculator helps you understand your estimated BAC level, but it should never be used as the sole factor in deciding whether to drive. Individual variation, medication interactions, fatigue, and other factors mean that you may be more impaired than your BAC number suggests. Always plan for a designated driver or alternative transportation when drinking any amount of alcohol.

Formulas

Widmark BAC Formula

BAC = (Alcohol in grams / (Body weight in grams × r)) − (0.015 × hours)

The standard Widmark formula for estimating blood alcohol content, where r is the gender-specific Widmark factor (0.68 for males, 0.55 for females) and 0.015 is the average metabolism rate per hour.

Alcohol Grams from Drinks

Alcohol (g) = Volume (mL) × ABV (decimal) × 0.789

Calculates the grams of pure alcohol in a beverage. Multiply the drink volume in milliliters by the alcohol by volume fraction, then by 0.789 (the density of ethanol in g/mL).

Time to Sober

Hours to 0.00% = Current BAC / Metabolism Rate

Estimates how many hours until BAC returns to zero. The average metabolism rate is 0.015% per hour, though it ranges from 0.010% to 0.020% depending on the individual.

Standard Drinks

Standard Drinks = Alcohol (g) / 14

Converts total alcohol consumed into standard drink equivalents. In the United States, one standard drink contains 14 grams of pure alcohol.

Reference Tables

BAC Levels and Effects

Impairment effects at different blood alcohol content levels, from minimal effects to life-threatening danger.

BAC Range	Level	Typical Effects
0.00 – 0.02%	Sober / Minimal	Normal behavior; subtle mood elevation
0.02 – 0.05%	Relaxation	Mild euphoria; slight reduction in inhibitions and visual function
0.05 – 0.08%	Buzzed	Lowered alertness; reduced coordination and emergency response
0.08 – 0.10%	Legally Impaired	Impaired balance, speech, vision, and reaction time
0.10 – 0.15%	Intoxicated	Significant motor control loss; slurred speech
0.15 – 0.20%	Severely Impaired	Major loss of balance; risk of nausea and vomiting
0.20 – 0.30%	Dangerously Intoxicated	Confusion; possible blackout; risk of aspiration
0.30%+	Life Threatening	Loss of consciousness; risk of coma and respiratory failure

Standard Drink Equivalents by Beverage Type

Common alcoholic beverages and their equivalent number of standard drinks (1 standard drink = 14 g pure alcohol).

Beverage	Typical Serving	ABV	Standard Drinks
Regular Beer	12 oz (355 mL)	5%	1.0
Light Beer	12 oz (355 mL)	4.2%	0.8
Craft / IPA	12 oz (355 mL)	7%	1.4
Wine	5 oz (148 mL)	12%	1.0
Spirits (Shot)	1.5 oz (44 mL)	40%	1.0
Double Shot	3 oz (89 mL)	40%	2.0
Margarita	6 oz (177 mL)	13%	1.3
Long Island Iced Tea	8 oz (237 mL)	22%	3.0

Worked Examples

180 lb Male After 3 Beers in 2 Hours

A 180 lb (81,647 g) male drinks 3 regular beers (12 oz each, 5% ABV) over 2 hours on an empty stomach.

Calculate alcohol per beer: 355 mL × 0.05 × 0.789 = 14.0 g

Total alcohol: 3 × 14.0 = 42.0 g

Apply Widmark formula: BAC = 42.0 / (81,647 × 0.68) = 42.0 / 55,520 = 0.000756 = 0.0756%

Subtract metabolism: 0.0756 − (0.015 × 2) = 0.0756 − 0.030 = 0.0456%

Time to sober: 0.0456 / 0.015 = 3.04 hours

Estimated BAC is 0.046%, classified as Relaxation level. Under the US legal limit of 0.08%. Approximately 3 hours until BAC returns to 0.00%.

130 lb Female After 2 Glasses of Wine in 1 Hour

A 130 lb (58,967 g) female drinks 2 glasses of wine (5 oz each, 12% ABV) over 1 hour on a light meal.

Calculate alcohol per glass: 148 mL × 0.12 × 0.789 = 14.0 g

Total alcohol: 2 × 14.0 = 28.0 g

Apply Widmark formula: BAC = 28.0 / (58,967 × 0.55) = 28.0 / 32,432 = 0.000863 = 0.0863%

Subtract metabolism: 0.0863 − (0.015 × 1) = 0.0713%

Light meal adjustment reduces peak BAC by approximately 25%: 0.0713 × 0.75 = 0.0535%

Estimated BAC is approximately 0.054%, classified as Buzzed level. Under the US legal limit but impairment to coordination is present. Approximately 3.6 hours until BAC returns to 0.00%.

How to Use the BAC Calculator

Enter Your Physical Details

Select your gender (male or female) and enter your body weight in pounds or kilograms. Gender determines the Widmark distribution factor used in the calculation, and weight affects how alcohol is diluted across your body mass. These two inputs have the greatest impact on your BAC estimate.

Add Your Drinks

Click Add Drink to log each beverage you consumed. Select the drink type (beer, wine, spirits, or cocktail), choose a preset or enter a custom size in ounces, and set the ABV (alcohol by volume) percentage. Add multiple entries if you had different types of drinks. Use the cocktail presets for popular mixed drinks with pre-filled ABV values.

Set Time and Conditions

Enter the total time since your first drink in hours and minutes. Select your stomach contents level: empty stomach means full alcohol absorption, a light meal reduces peak BAC by about 25%, and a full meal can reduce it by up to 50%. Optionally adjust the metabolism rate slider if you know your body processes alcohol faster or slower than average.

Review Your Results

Click Calculate BAC to see your estimated blood alcohol content, impairment level with effects description, time until your BAC returns to zero, peak BAC reached during the session, and a visual timeline showing your projected BAC decline. Compare your result against your country's legal driving limit. Use the export or print buttons to save your results.

Frequently Asked Questions

How does the BAC calculator work?

This calculator uses the Widmark formula, the most widely accepted scientific method for estimating blood alcohol content. The formula takes the total grams of pure alcohol you consumed (calculated from drink volumes and ABV percentages), divides it by your body weight multiplied by a gender-specific distribution constant (0.68 for males, 0.55 for females), then subtracts the alcohol your body has metabolized over time at a rate of approximately 0.015% per hour. The result is your estimated BAC as a percentage. The calculator also factors in stomach contents, which affect absorption rate. A full meal can reduce peak BAC by up to 50% compared to drinking on an empty stomach. While the Widmark formula is reliable for most people, individual results may vary based on genetics, medications, and health factors.

What is the legal BAC limit for driving?

Legal BAC limits vary by country and driver type. In the United States, the legal limit is 0.08% for adult drivers (21 and over), 0.04% for commercial vehicle operators, and effectively 0.00% to 0.02% for drivers under 21 (zero-tolerance laws). The United Kingdom and Canada also use 0.08%, while Australia and Germany set a stricter limit of 0.05%. Japan enforces 0.03%, and Sweden has one of the world's lowest limits at 0.02%. It is important to understand that impairment begins at BAC levels well below the legal threshold. Research shows reduced visual function and divided attention at just 0.02%. The legal limit represents the enforcement threshold, not a safe level for driving.

How long does it take for alcohol to leave your system?

Your body metabolizes alcohol at a roughly constant rate of 0.010% to 0.020% BAC per hour, with the average being about 0.015% per hour. This means if your BAC is 0.08%, it would take approximately 5 hours and 20 minutes to return to 0.00%. At 0.15% BAC, you would need roughly 10 hours. Nothing can speed up this process — not coffee, cold showers, food, or exercise. These may make you feel more alert, but they do not reduce your BAC. Your liver processes alcohol at a fixed rate determined by your enzyme levels. The only factor that truly reduces BAC is time. Sleep does not speed up metabolism either, but it gives your body the time it needs to process the remaining alcohol.

Does eating food affect your BAC?

Yes, food has a significant effect on your BAC. Eating before or while drinking slows the rate at which alcohol is absorbed into your bloodstream by delaying gastric emptying — the process by which stomach contents pass into the small intestine where most alcohol absorption occurs. Drinking on an empty stomach allows alcohol to reach the small intestine quickly, producing a higher and faster peak BAC. A light meal or snack can reduce peak BAC by approximately 25%, while a substantial meal (especially one containing fats, proteins, and carbohydrates) can reduce peak BAC by up to 50%. However, food only slows absorption; it does not prevent it. The same total amount of alcohol will eventually be absorbed regardless of food intake. The benefit is a lower, more gradual peak that gives your liver more time to metabolize the alcohol.

How accurate is this BAC calculator?

BAC calculators using the Widmark formula provide reasonable estimates for most people but are not precise to the level of a blood test or calibrated breathalyzer. The formula is based on population averages for body water content and metabolism rates, which can vary significantly between individuals. Factors like genetics, liver health, medications (including common ones like aspirin and antacids), hydration level, and chronic alcohol use patterns all influence actual BAC but are not captured by the formula. Studies suggest the Widmark method is typically accurate within plus or minus 0.01% to 0.02% for moderate drinkers. For safety-critical decisions like driving, always treat the estimate as approximate and err on the side of caution. This calculator is an educational tool, not a substitute for a certified breathalyzer or medical assessment.