Blood Alcohol Content (BAC) Estimator

Estimate blood alcohol content free online using the standard Widmark formula. An educational approximation only -- never use any BAC estimate to decide whether driving is safe.

Never drive after drinking, regardless of any number shown here

This is a rough educational estimate only. Real impairment begins before BAC reaches any legal threshold, and individual metabolism varies in ways this formula cannot capture.

Body Weight (kg)

Sex

Standard Drinks Consumed

Hours Since First Drink

Browser only. Educational approximation -- not a basis for any decision about driving.

How to Use This Tool

Enter weight and sexUsed in the standard Widmark formula

Enter drinks and time elapsedStandard drinks and hours since starting

See the rough estimateTreat as educational only, never for driving decisions

Blood Alcohol Content (BAC) Estimator is a free online tool that works entirely in your browser — no signup, no data uploaded, no limits.

An Educational Approximation, Never a Safety Determination

The Widmark formula has been used for decades as a standard approximation method for blood alcohol content, but it remains exactly that -- an approximation based on population averages for weight and metabolism. It cannot capture individual variation in how a specific person's body processes alcohol, which is precisely why no calculated number from this or any similar tool should ever inform a decision about whether driving is safe.

Impairment Begins Before Any Calculated Number Suggests It

Reaction time, judgment, and coordination all begin degrading at BAC levels below commonly cited legal limits, and individual sensitivity varies. There is no calculated number from a formula like this that reliably indicates safety to drive -- the only consistently safe choice after drinking any amount is not driving at all.

What This Tool Is Actually For

Understanding roughly how factors like body weight, time, and drink count interact in alcohol metabolism has general educational value. This tool is not designed or intended to help calibrate drinking to stay under any particular number, since that framing fundamentally misunderstands both the formula's limitations and the actual safety risks involved.

Frequently Asked Questions

No, and this is the single most important thing to understand about this tool. Individual alcohol metabolism varies significantly based on factors this formula cannot capture, and impairment to driving ability begins before BAC reaches any legal threshold. The only reliable way to ensure safety is not driving after drinking at all -- never use a calculated number to decide otherwise.

The Widmark formula, a long-standing standard approximation: BAC = (Alcohol grams / (Body weight grams x distribution ratio)) - (Hours x metabolism rate). It's a population-average approximation, not a precise measurement of your actual individual BAC at any moment.

Real BAC depends on factors including food consumption, medication interactions, individual metabolism rate, hydration, and even genetic variation in alcohol-processing enzymes -- none of which a simple formula based on weight, drinks, and time can fully capture.

Do not drive. Arrange alternative transportation -- a rideshare, a designated sober driver, or staying where you are -- regardless of how much time has passed or what any calculator estimates. This is the only response that reliably avoids the serious risks of impaired driving.

No. This is an educational tool for understanding roughly how alcohol metabolism works, not a tool for calibrating drinking to stay under any threshold. Impairment and legal risk both exist well before commonly cited legal BAC limits.