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Blood Alcohol Content (BAC) Calculator

Estimate your blood alcohol content (BAC) from drinks consumed, weight, and gender, plus roughly how long until you're sober.

ESTIMATES ONLY - DO NOT USE TO DETERMINE FITNESS TO DRIVE

This calculator provides rough estimates based on average metabolic rates. It cannot account for your personal genetics, food intake, metabolism, or tolerance. Never use these results to make safety decisions or determine if you are legally allowed to drive. If you drink, please do not drive.

Body water percentage differs by biological sex, which affects alcohol distribution.

Hours

Since first drink

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Add your drinks and personal details, then hit calculate to see your estimated BAC.

Formula Reference

BAC Formula

The Widmark formula estimates Blood Alcohol Concentration by dividing the total grams of alcohol consumed by body weight adjusted for a gender-based body-water distribution constan...

$$BAC\% = \frac{\text{Alcohol Consumed (g)}}{\text{Body Weight (g)} \times r} \times 100 - (0.015 \times \text{Hours})$$
View Full Formula, Step-by-Step Guide & Worked Examples

Alcohol Metabolism & Effects

Understanding how your body processes alcohol.

Elimination Rate

The average human body eliminates alcohol at a rate of roughly 0.015% per hour. Nothing speeds this up—not coffee, cold showers, or exercise. Only time can sober you up.

Food & Absorption

Drinking on an empty stomach causes rapid absorption, leading to a quick spike in BAC. Eating a large meal before drinking slows the absorption rate, giving your liver more time to process the alcohol.

Impairment Begins Early

Cognitive impairment, reduced reaction time, and loss of fine motor skills begin at BAC levels as low as 0.02%, long before you hit the legal driving limit.

Education

How the Widmark BAC Formula Works

01

The Widmark Formula

This calculator estimates blood alcohol content using the Widmark formula: BAC = [alcohol consumed in grams / (body weight in grams x r)] x 100, then subtracts an average metabolic elimination rate of 0.015% per hour since drinking started. The constant r represents body water distribution and is set to 0.68 for men and 0.55 for women, with the average of both used for other genders.

02

Why Estimates Can Differ From Real BAC

The Widmark formula assumes an empty stomach and average metabolism, so real BAC can vary with food intake, liver function, medications, and individual body composition. Because of this, the tool is intended for general awareness only and should never be used to decide whether it is safe or legal to drive.

03

Worked BAC Example

For an 80 kg man who consumes three standard drinks (about 42 grams of alcohol total) over two hours, the estimate is roughly (42 / (80,000 x 0.68)) x 100 = 0.077%, minus 0.03% eliminated over two hours, leaving an estimated BAC near 0.047%. Time to reach 0.00% is then found by dividing the remaining BAC by the 0.015% hourly elimination rate.

04

Track Related Health Metrics

Alcohol calories add up quickly, so pairing this tool with the Calorie Calculator helps account for extra energy intake from drinking. The Healthy Weight Range Calculator can also help track how weight is affected by regular alcohol consumption over time.

Good to know

Questions, answered

Quick answers about how this tool works.

This tool uses the widely accepted Widmark Formula. It calculates the total grams of alcohol consumed, distributes it based on body water percentage (which differs by gender), and then subtracts the average metabolic elimination rate (typically 0.015% per hour) for the time passed since drinking started.

Many factors can cause your actual BAC to differ from estimates, including: whether you ate food before or during drinking, your genetics and liver health, individual metabolic rate variations, the use of medications or other drugs, and even your stress or fatigue levels.

Legal limits vary significantly by country and region. For example, it is 0.08% in the United States, UK (excluding Scotland), and Canada. It is 0.05% in many European countries and Australia, and 0.00% (zero tolerance) in several others. Always check your local laws, and remember that impairment starts well below the legal limit.

BAC measures the percentage of alcohol in a person's bloodstream. A BAC of 0.08% is the legal driving limit in many countries.

On average, the body metabolizes alcohol at a rate of about 0.015% BAC reduction per hour. Water and coffee do not speed this up.

Guides

Related guides

Plain-language explainers that sit next to this tool.

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