BAC Calculator – Blood Alcohol Concentration Estimator
Estimate your blood alcohol concentration (BAC) using the Widmark Equation based on your body weight, sex, number of standard drinks, and time elapsed.
BAC Calculator Tool
Enter your details below and press Calculate BAC to see your estimated blood alcohol concentration and impairment level.
This BAC calculator estimates your blood alcohol concentration based on body weight, sex assigned at birth, number of standard drinks, and hours since your first drink. Results are for informational and educational purposes only and are not a substitute for a certified breathalyzer or blood test.
Enter a body weight greater than 0.
Used to apply the Widmark distribution ratio. Validated equations for trans and non-binary individuals are not currently available.
1 standard drink ≈ 14g of pure alcohol (12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits).
Number of drinks cannot be negative.
Hours cannot be negative.
Estimated BAC
Blood alcohol concentration: 0.050%
Estimated Impairment Level
Level: Moderate
Comparison to Common Legal Limit
Vs. 0.08% limit: Below 0.08%
This is a comparison to a common legal limit, not a legal or safety determination. Never drive after drinking, regardless of this estimate.
Important:
BAC Calculator vs Blood Alcohol Calculator
A BAC calculator, sometimes referred to as a blood alcohol calculator estimates the amount of alcohol in your bloodstream based on factors such as body weight, sex assigned at birth, alcohol consumed, and time elapsed since drinking began. While these terms are often used interchangeably, both tools provide only an estimate and cannot replace a certified breathalyzer or laboratory blood test. .Need to Dilute Spirits?
If you’re working with high-proof spirits, try the Alcohol Dilution Calculator to calculate the exact amount of water needed to reach your desired ABV.
About the BAC Calculator
The BAC calculator estimates blood alcohol concentration using the Widmark Equation, a formula widely used in toxicology and alcohol research. It factors in body weight, sex assigned at birth, the number of standard drinks consumed, and the time elapsed since drinking began. It is designed for educational purposes, to help build awareness of how alcohol affects the body — not as a tool for determining whether it is legal or safe to drive.
How to use the BAC calculator
- Enter your body weight and select the unit (kg or lbs).
- Select your sex assigned at birth (male or female).
- Enter the number of standard drinks consumed (1 standard drink ≈ 14g of pure alcohol, e.g., 12 oz of 5% beer).
- Enter the hours since your first drink.
- Select Calculate BAC to see your estimated blood alcohol concentration and impairment level.
Note: This calculator uses equations based on sex assigned at birth due to limitations in current scientific data. Validated equations for transgender or non-binary individuals are not currently available.
The Science Behind Blood Alcohol Concentration
Blood alcohol concentration (BAC) measures the grams of alcohol present per 100 mL of blood, expressed as a percentage. The Widmark Equation estimates BAC using the formula below.
Where each term means:
- Dose: total alcohol consumed, in grams (1 standard drink ≈ 14g of ethanol).
- Weight: body weight, converted to grams.
- r (distribution ratio): approximately 0.68 for men and 0.55 for women, reflecting average differences in body water content.
- 0.016: the average rate at which BAC decreases per hour as the body metabolizes alcohol.
Alcohol absorption typically takes 30 to 70 minutes, and higher BAC levels generally correspond to greater impairment. For more on alcohol-impaired driving, see the National Highway Traffic Safety Administration (NHTSA) guide on drunk driving.
Common BAC Levels and Effects
Different estimated BAC levels are generally associated with different stages of impairment:
0.02–0.03%
Light buzz, slight relaxation, minor mood changes.
0.04–0.06%
Lowered judgment, relaxed inhibitions, reduced coordination.
0.08%
Common legal driving limit in many regions; significant impairment of balance and reaction time.
0.10–0.12%
Marked impairment of motor control, slurred speech, slowed reactions.
0.20%+
High risk of blackout, vomiting, and severe intoxication; medical risk increases.
These ranges are general guidelines. Individual responses to alcohol vary based on tolerance, health conditions, medications, and other factors.
Frequently Asked Questions About BAC
How accurate is the BAC calculator?
The BAC calculator uses the Widmark Equation to produce a reasonable estimate based on body weight, sex, number of standard drinks, and time elapsed. Individual factors such as metabolism, food intake, medication, and overall health can cause your actual BAC to differ. Certified breathalyzers or blood tests are required for legal or medical purposes.
What counts as a standard drink for BAC calculations?
A standard drink contains about 14 grams of pure alcohol. That is roughly equal to 12 oz of 5% ABV beer, 5 oz of 12% ABV wine, or 1.5 oz of 40% ABV spirits.
Why does sex affect BAC estimates?
The Widmark Equation uses a distribution ratio of about 0.68 for men and 0.55 for women to account for average differences in body water content, which affects how alcohol is diluted in the body and therefore the resulting BAC.
What BAC level is the legal driving limit?
In many countries and US states, 0.08% BAC is the legal limit for driving, though some jurisdictions set lower limits, such as 0.05% or zero tolerance for certain drivers. This calculator provides an estimate only and should never be used to decide whether it is safe to drive.
How does the body eliminate alcohol over time?
On average, the body eliminates alcohol at a rate of about 0.015 to 0.017 percent BAC per hour, though this varies by individual. This calculator uses an average elimination rate of 0.016% per hour in its estimate.
Can this BAC calculator tell me if it’s safe to drive?
No. This calculator provides an educational estimate of blood alcohol concentration only. It cannot account for individual variation, food intake, medication, or health conditions, and it should never be used to decide whether driving is safe. The only safe choice after drinking is not to drive.