Is a BAC calculator accurate enough for driving decisions?

No. It is only an estimate. BAC can keep rising after drinking stops, and reaction time, judgment and coordination can be impaired below common legal limits.

What is the Widmark formula?

It estimates BAC from grams of ethanol, body weight, a body-water distribution factor and elapsed time. It is useful for rough education, not for legal or medical proof.

What are alcohol overdose warning signs?

Seek urgent help for confusion, inability to stay conscious, vomiting, seizures, slow or irregular breathing, pale or clammy skin, low body temperature or suspected alcohol poisoning.

BAC Calculator

Estimate blood alcohol concentration from drinks, body weight, biological sex and time using a Widmark-style model. For safety education only, never for deciding whether to drive.

Sex

Weight (lb)

Time since drinking (hours)

Reference point

Drinks

Preset

Volume (mL)

ABV (%)

Servings

What this BAC calculator estimates

This tool estimates blood alcohol concentration after drinking. It is not a breath test, blood test, legal defense, medical diagnosis or permission to drive. Real BAC can differ because of food, drink timing, body composition, medications, liver health and inaccurate pour sizes.

ethanol_{g} = V_{m L} \times A B V \times 0.789

Pure ethanol estimate from beverage volume, alcohol by volume and ethanol density.

BAC_{%} = \frac{A _{g}}{W _{g} \times r} \times 100 - β t

Widmark-style blood alcohol estimate after subtracting metabolism over time.

Never use an estimate to decide whether to drive

Driving impairment can begin below legal limits, and BAC may still be rising after the last drink. Use a sober ride, rideshare or another safe option if you drank alcohol.

How to read BAC units

BAC unit	Meaning
0.08%	0.08 grams of alcohol per deciliter of blood
80 mg/dL	The same concentration expressed in milligrams per deciliter
0.8 per mille	The same concentration expressed as per mille

In the United States, 0.08 g/dL is a common per se driving limit for many adult drivers, but impairment and legal risk can occur below that level and special rules may apply.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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