Blood Alcohol Content (BAC) Estimator
Example: 2 beers + 2 hours → ~0.04% BAC
Estimate your blood alcohol content using the Widmark formula. This calculator considers your sex, body weight, drinks consumed (with volume and alcohol percentage), and time elapsed since your first drink. This is for educational purposes only and should not be used to determine fitness to drive.
🍺 Drink 1
🍷 Drink 2
🥃 Drink 3
Modeled decline from peak BAC
Current BAC
Estimated blood alcohol content
Time to 0.00%
Estimated time until sober
Risk Level
General impairment level (not legal advice)
Model Note
Important simplification used by this estimate
How We Calculate This
Uses a simplified instant-peak Widmark model: Peak BAC = (grams alcohol / (body weight in grams × r)) × 100 × absorption factor. Absorption factor is 1.0 for standard/food-in-stomach and 1.1 for empty stomach. Current BAC = max(0, peak BAC - 0.015 × hours elapsed). Body water constant (r): male = 0.68, female = 0.55. Grams of alcohol = volume (mL) × ABV × 0.789 (ethanol density). The 0.015%/hour elimination rate is an average; actual rates vary from 0.010-0.020%/hour.
Methodology last reviewed: July 2026. How SparkCalc works
Sources: NHTSA – Drunk Driving: Blood Alcohol Concentration (BAC)
Frequently Asked Questions
How accurate is this BAC calculator?
This calculator uses the Widmark formula, which provides a rough estimate. Actual BAC varies based on many factors including metabolism, food intake, medications, and individual physiology. Never use this to determine if you are safe to drive.
What is the Widmark formula?
The Widmark formula calculates peak BAC as: BAC = (Alcohol in grams / (Body weight in grams × r)) × 100, where r is the body water constant (0.68 for males, 0.55 for females). BAC decreases at approximately 0.015% per hour.
What do the risk levels mean?
These are general impairment levels, not legal limits. Below 0.02% shows minimal effects. 0.02-0.05% may show mild impairment. 0.05-0.08% shows significant impairment. Above 0.08% is very high risk. Legal limits vary by jurisdiction.
Why does empty stomach matter?
In real life, food can slow alcohol absorption. This simplified calculator does not model delayed absorption or a later peak; it applies a documented 10% peak BAC multiplier for empty stomach estimates.
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IMPORTANT: Never drive after consuming ANY amount of alcohol. This calculator is for educational purposes only and should NEVER be used to determine fitness to drive. Actual BAC varies significantly between individuals based on metabolism, medications, food intake, and many other factors. Even at low BAC levels, alcohol impairs judgment, reaction time, and decision-making. If you have consumed alcohol, use a designated driver, taxi, or rideshare service.