BAC Calculator

Your Details

Sex

Body Weight (kg)

Standard Drinks Consumed

Hours Since First Drink

Widmark Formula

Blood Alcohol Content

BAC = (Alcohol Consumed in grams ÷ (Body Weight in grams × r)) × 100 − (0.015 × Hours)

Where:
r = 0.68 for men, 0.55 for women (body water distribution ratio)
1 standard drink ≈ 14 grams of pure alcohol
0.015 = average BAC eliminated per hour

Worked Example

Male, 75kg, 3 standard drinks, 2 hours elapsed

Alcohol grams = 3 × 14 = 42g
Body weight in grams = 75,000g
BAC = (42 ÷ (75,000 × 0.68)) × 100 − (0.015 × 2)
BAC = 0.0824% − 0.030% = 0.052%

US Legal Reference Points

0.02%: Some impairment begins
0.05%: Reduced coordination, judgment affected
0.08%: Legal driving limit in most US states
0.15%+: Severe impairment, high risk

Common Scenarios

Male, 75kg, 3 drinks, 2 hours

BAC ≈ 0.052%

Female, 60kg, 2 drinks, 1 hour

BAC ≈ 0.070%

Male, 90kg, 5 drinks, 3 hours

BAC ≈ 0.069%

Female, 65kg, 4 drinks, 2 hours

BAC ≈ 0.127%

Frequently Asked Questions

This calculator provides an estimate based on the Widmark formula, a well-established model, but your actual BAC can vary based on factors like food intake, medications, liver function, hydration, and individual metabolism. It should never be used as a precise measurement or as the basis for deciding whether it is safe to drive - only a breathalyzer or blood test gives an accurate reading.

In most US states, the legal limit for driving is 0.08% BAC for drivers 21 and over, though some states and commercial drivers face stricter limits. However, impairment to reaction time, judgment, and coordination can begin well below 0.08%, and many countries have lower legal limits (0.05% or 0.02%) or zero-tolerance policies for certain driver categories.

The Widmark formula uses different distribution ratios for men and women (0.68 for men, 0.55 for women) because women generally have a higher proportion of body fat and lower proportion of body water relative to body weight than men. Since alcohol distributes through body water, this typically results in women reaching a higher BAC than men after consuming the same amount of alcohol at the same body weight.

Food does not reduce the total amount of alcohol that eventually enters your bloodstream, but it does slow the rate of alcohol absorption, which can lower your peak BAC and spread out its effects over a longer period. This calculator does not account for food intake, so actual peak BAC when drinking on a full stomach may be somewhat lower than the estimate shown here.

The body eliminates alcohol at a fairly consistent average rate of about 0.015% BAC per hour, regardless of how much was consumed. This means a BAC of 0.08% takes roughly 5-6 hours to fully clear, and this elimination rate cannot be meaningfully sped up by coffee, cold showers, or exercise - time is the only reliable way to lower BAC.

BAC Calculator - Understanding Blood Alcohol Content Estimation

Blood Alcohol Content (BAC) represents the percentage of alcohol in a person's bloodstream, and it's the standard measurement used by law enforcement and researchers to gauge alcohol-related impairment. This calculator uses the Widmark formula, a long-established estimation model from alcohol research, to provide an educational approximation - but it's important to understand upfront that this is only an estimate, not a substitute for an actual breathalyzer or blood test, and it should never be the basis for deciding whether driving is safe.

Safety first: The only truly safe BAC for driving is 0.00%. This calculator is for educational and awareness purposes only.

How the Widmark Formula Works

The Widmark formula estimates BAC based on the amount of alcohol consumed, body weight, biological sex, and time elapsed. It works by calculating the theoretical concentration of alcohol if it were evenly distributed through body water, using a distribution ratio (r) that differs between men and women, then subtracting the amount of alcohol the body has already metabolized based on the average elimination rate of about 0.015% per hour. While useful as an educational model, actual BAC can differ from this estimate due to factors the formula doesn't capture, including food intake, medication interactions, liver health, and individual metabolic variation.

Why the Same Number of Drinks Affects People Differently

Body weight and biological sex both significantly influence how a given amount of alcohol affects BAC. A larger body has more total body water to dilute the same amount of alcohol, generally resulting in a lower BAC for a heavier person compared to a lighter person consuming the same drinks. Women typically reach a higher BAC than men of the same weight after equivalent alcohol consumption, primarily due to differences in average body composition - women generally have a higher percentage of body fat and lower percentage of body water relative to total body weight, which concentrates alcohol more in the available body water.

What Actually Lowers BAC (and What Doesn't)

The body eliminates alcohol at a remarkably consistent rate, largely regardless of external factors - roughly 0.015% BAC per hour on average. This means popular folk remedies like drinking coffee, taking a cold shower, or exercising do not meaningfully speed up alcohol elimination; they may make a person feel more alert, but they don't reduce actual BAC or the underlying impairment. The only reliable way to lower BAC is time - a BAC of 0.08% takes roughly 5-6 hours to fully clear from the body under typical elimination rates.

Understanding "Standard Drinks"

This calculator uses the standard drink definition common in alcohol research: approximately 14 grams of pure alcohol, which roughly corresponds to a 12 oz (355 ml) regular beer (about 5% ABV), a 5 oz (148 ml) glass of wine (about 12% ABV), or a 1.5 oz (44 ml) shot of distilled spirits (about 40% ABV). Drinks with higher alcohol content, larger pour sizes, or mixed drinks with multiple shots can easily contain more than one standard drink's worth of alcohol, which is a common source of underestimating actual alcohol intake.

Why This Calculator Should Never Guide a Driving Decision

Individual variation is significant: Two people with identical weight, sex, and drink count can have meaningfully different actual BAC due to metabolism, food intake, and other individual factors this formula cannot account for.
Impairment begins before legal limits: Reaction time, judgment, and coordination can be measurably affected well below the 0.08% legal driving limit in most US states.
Only measured BAC is reliable: A breathalyzer or blood test measures actual BAC directly; this calculator only provides a rough estimate based on averages.
The safest choice is always zero: If you plan to drink, the safest and simplest approach is to arrange alternative transportation in advance, rather than relying on any BAC estimate to judge your own fitness to drive.

How this calculator works, and where the numbers come from

The BAC Calculator applies the standard formula for this calculation to the values you enter and updates the result as you type. The calculation itself happens in your browser, and the page explains the method so you can check any result by hand.

Please note: This tool gives general estimates based on published population formulas. It is not medical advice and does not replace assessment by a doctor, dietitian or other qualified professional.

Sources and further reading

Last reviewed: October 6, 2026 by the CalcQube Editorial Team. See our editorial policy for how we build and check calculators, or report an error.