Online BAC Calculator - Estimate Your Blood Alcohol Concentration

What Is This Tool?

The BAC Calculator gives a rough estimate of your blood alcohol content using the Widmark approach. You enter your gender and body weight, how long ago you had your first drink, and the number, serving size, and ABV of each drink — beer, wine, liquor, or other. It then estimates your current BAC as a percentage and how many hours until it would return to zero at a standard elimination rate. Weight can be entered in metric or imperial units, and the result can be downloaded as a PDF. The number is only an estimate and should never be used to decide whether you are fit to drive.

How to Use This Tool?

• Select your gender and enter your body weight.
• Enter how long ago you had your first drink.
• Add the number, size, and ABV of each drink type you consumed.
• Click Calculate to see your estimated BAC and the time until it reaches zero.

Key Features

• Estimates blood alcohol content from gender, body weight, drinks, and time elapsed.
• Accepts beer, wine, liquor, and other drinks, each with its own serving size and ABV.
• Offers preset serving sizes — bottles, cups, cans, and shots.
• Estimates the time until your BAC returns to zero.
• Metric/imperial weight toggle and one-click PDF download.

Examples

• Two 330 ml beers and one 330 ml glass of wine for an 80 kg person produce an estimated BAC after about 1.5 hours.
• A higher body weight lowers the estimated BAC for exactly the same drinks.
• More time since the first drink reduces the estimate as alcohol is metabolized.
• The time-to-zero figure divides the current BAC by the standard elimination rate.

Common Use Cases

• Getting a rough sense of how a few drinks may affect you.
• Understanding roughly how long alcohol may stay in your system.
• Comparing how serving size and ABV change the estimate.
• Learning how body weight and gender influence BAC.
• Planning ahead to arrange a safe ride or simply wait it out.

Tips & Best Practices

• Enter accurate serving sizes and ABV for a closer estimate.
• Count every drink, including partial ones.
• Remember the estimate ignores food, hydration, and individual metabolism.
• Never treat the result as proof that you are safe to drive.
• When in doubt, don't drive — arrange another way home.

Limitations

• BAC varies widely between people; food, medication, health, and metabolism all change the real value.
• It must never be used to decide whether you are fit to drive or operate machinery.
• It isn't medical or legal advice and can't replace an actual breath or blood test.
• Nothing is saved between sessions — only the current result can be exported as a PDF.

Frequently Asked Questions

How is BAC estimated?

It uses the Widmark approach: total alcohol consumed relative to body weight and a distribution factor, minus the amount your body has eliminated over time.

Can I rely on this to decide whether to drive?

No. It is only a rough estimate and should never be used to judge whether you can legally or safely drive.

Why do gender and weight matter?

They affect how alcohol distributes in the body, so the same drinks produce different BAC levels in different people.

What does "time to zero" mean?

An estimate of how many hours until your BAC would return to zero at a standard elimination rate.

Key Terminology

Blood Alcohol Content (BAC)

The percentage of alcohol present in the bloodstream.

ABV

Alcohol by volume — the percentage of pure alcohol in a drink.

Widmark formula

A standard method for estimating BAC from alcohol consumed and body weight.

Elimination rate

The roughly constant rate at which the body clears alcohol, about 0.015% per hour.

Standard serving

A defined drink size — bottle, cup, can, or shot — used to estimate the alcohol consumed.

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