Curious what your BAC might be? Use the calculator above to get an estimate based on your drinks, weight, and gender. Enter your details, and the tool returns an approximate blood alcohol content within seconds.
This BAC calculator uses the Widmark formula, the most widely accepted method for estimating blood alcohol concentration. It gives you a ballpark number for planning purposes. It is not a breathalyzer, a medical test, or legal proof of sobriety.
How the Blood Alcohol Calculator Works
The calculator takes a few inputs: the number of standard drinks you consumed, your body weight, your gender, and how much time has passed since you started drinking. It then applies the Widmark equation to estimate your BAC.
Here is the simplified version of that formula:
BAC = (Alcohol consumed in grams / (Body weight in grams × r)) − (0.015 × hours since first drink)
The variable r is a gender-based constant. It accounts for differences in body water distribution. For males, r is typically 0.68. For females, it is typically 0.55.
The 0.015 subtracted per hour reflects average alcohol metabolism. Most people eliminate roughly one standard drink per hour, though this varies.
Calculate Your Blood Alcohol Concentration
Number of standard drinks you consume
The calculator asks how many standard drinks you have had. This is the single biggest factor in your estimated BAC. More drinks means more grams of alcohol entering your bloodstream.
Be honest and precise here. A "drink" at a bar or party is often larger than a standard drink. A strong craft IPA in a pint glass can equal nearly two standard drinks. A generous wine pour can be 1.5 or more.
If you are unsure, round up. Underestimating drink count is the most common reason BAC estimates come in too low.
Weight, gender, and other factors that approximate BAC
Body weight matters because alcohol distributes through body water. A heavier person has more volume for the alcohol to dilute into, resulting in a lower BAC from the same number of drinks.
Gender affects the calculation because of body composition differences. Women generally have a higher percentage of body fat and a lower percentage of body water than men of the same weight. This means alcohol concentrates more in a smaller water volume, producing a higher BAC.
Other factors the calculator cannot fully capture include:
- Amount of food in your stomach. Eating before or while drinking slows alcohol absorption.
- Metabolism rate. Individual liver enzyme activity varies. The calculator uses an average rate of 0.015 per hour.
- Age and overall health. Older adults and people with certain health issues may process alcohol more slowly.
- Medications. Some drugs slow metabolism or amplify alcohol's effects.
Because of these numerous factors, every BAC calculator produces an estimate, not a measurement.
What Is Blood Alcohol Content?
Blood alcohol content is the measure of alcohol present in your bloodstream. Law enforcement, medical professionals, and researchers all use BAC as the standard metric for intoxication.
Blood alcohol concentration as a percentage
BAC is expressed as a percentage of alcohol in your blood. Specifically, it represents grams of alcohol per 100 ml of blood. A BAC of 0.08 means 0.08 grams of alcohol per 100 ml of blood.
Here are some reference points:
- 0.00% means no measurable alcohol in your blood.
- 0.02% is a light, relaxed feeling for most people.
- 0.08% is the legal limit for drivers age 21 and over in all 50 U.S. states.
- 0.15% and above indicates severe impairment.
- 0.30%+ carries risk of loss of consciousness or worse.
How alcohol concentration builds in your blood
When you consume alcohol, it passes through your stomach and small intestine into your bloodstream. Peak BAC typically occurs 30 to 70 minutes after your last drink, depending on stomach contents and drink speed.
Your liver then metabolizes the alcohol at a roughly constant rate, about 0.015 per hour for most people. This means BAC drops in a straight line over time rather than a curve.
If you drink faster than your liver can process, your BAC climbs. That is why spacing drinks and eating food both help keep your blood alcohol concentration lower.
What Is a Standard Drink of Beer, Wine, and Liquor?
A standard drink contains approximately 14 grams of pure alcohol. This is the baseline the calculator uses. The container size changes depending on the beverage because each type has a different alcohol by volume (ABV).
Alcohol by volume and how to measure each drink
| Beverage | Typical ABV | Standard Drink Size |
|---|---|---|
| Beer | ~5% | 12 fl oz |
| Wine | ~12% | 5 fl oz |
| Distilled spirits (liquor) | ~40% | 1.5 fl oz |
These are guidelines, not absolutes. A 9% double IPA in a 16 oz pint is roughly 2.4 standard drinks. A 6 oz pour of 14% red wine is about 1.4 standard drinks.
To measure more accurately:
- Check the ABV on the label.
- Note the actual volume of your pour or can.
- Multiply ABV × volume (in ounces) × 0.6. Divide by 0.6 oz (the alcohol in one standard drink) to get your standard drink count.
Getting this right makes the BAC calculator far more useful.
BAC Effect and Impairment at Each Level
Alcohol affects your brain in a predictable progression. Here is what research generally associates with each BAC level:
- 0.01 to 0.03: Subtle relaxation. Minimal measurable impairment.
- 0.04 to 0.06: Lowered inhibitions, mild euphoria, and slightly reduced motor control.
- 0.07 to 0.09: Impaired balance, speech, reaction time, and judgment. At 0.08, it is illegal to drive in every U.S. state.
- 0.10 to 0.12: Clear deterioration of motor control and judgment. Slurred speech is common.
- 0.13 to 0.19: Major impairment to coordination and perception. Risk of blackout increases.
- 0.20 to 0.29: Disorientation, nausea, and inability to stand or walk without help. Memory blackout is likely.
- 0.30 and above: Risk of loss of consciousness, respiratory depression, and death.
Individual tolerance does not change BAC or its physiological effects. A "high tolerance" means your brain has adapted to functioning under impairment. It does not mean your BAC is lower or that you are safe to drive or operate machinery.
How alcohol and other drugs increase impairment
Mixing alcohol and other drugs, whether prescription, over the counter, or recreational, can multiply impairment beyond what BAC alone would predict. Common interactions include:
- Sedatives and benzodiazepines: Dramatically increase drowsiness and respiratory depression.
- Opioids: Combined depressant effects raise overdose risk.
- Antihistamines: Heighten drowsiness and slow reaction time.
- Stimulants: Can mask the feeling of intoxication without lowering BAC, leading people to drink more.
This calculator does not account for drug interactions. If you have taken any medication or substance alongside alcohol, your actual impairment may be significantly worse than the BAC estimate suggests.
Can You Drink and Drive? Legal BAC Limits
In the United States, it is illegal to drive with a BAC of 0.08 or higher if you are 21 or older. But lower thresholds apply in many situations:
- Under the legal drinking age of 21: Most states enforce a zero-tolerance policy, typically 0.00 to 0.02.
- Commercial drivers: The federal limit is 0.04.
- Utah: The legal limit is 0.05 for all drivers.
Many countries also set limits at 0.05 or lower. Check local laws before assuming 0.08 is universal.
Important: even a BAC below the legal limit can impair your ability to drive or operate machinery. Impairment begins well before 0.08. A BAC of 0.05 already reduces coordination and increases crash risk.
If the calculator shows any measurable BAC, the safest choice is not to drive.
Why This BAC Estimate Is Approximate
No online calculator can replace a breathalyzer or blood test. This tool uses population averages and a simplified formula. Your actual BAC can vary because of many factors:
- Individual metabolism differs. The 0.015 per hour rate is an average, not your personal rate.
- Stomach contents, hydration, fatigue, and body composition all shift real results.
- Drink strength can be hard to estimate, especially with mixed drinks and craft beverages.
- The calculator assumes you reported drink count and timing accurately.
This BAC calculator is for educational purposes only. It is not medical advice, legal counsel, or a substitute for a certified testing device. If you need a precise BAC reading for any reason, use an approved breathalyzer or contact a medical professional.
Blood Alcohol Content Calculator FAQs
How do I calculate BAC after one drink?
For a rough estimate after one standard drink, plug these numbers into the Widmark formula. A 160 lb male drinking one standard drink (14 grams of pure alcohol) would calculate:
BAC = 14 / (72,575 × 0.68) = approximately 0.028
After one hour of metabolism (subtract 0.015), the estimated BAC drops to about 0.013. After two hours, it is near zero.
A lighter person or a female would see a higher number from the same drink. The easiest approach is to enter your details in the calculator above rather than doing the math by hand.
How long after you consume alcohol does BAC drop?
Your BAC begins to drop as soon as your liver starts metabolizing alcohol, which happens continuously. The average person's BAC decreases by about 0.015 per hour.
That means if your BAC peaks at 0.08, it takes roughly five to six hours to return to 0.00. Drinking water, eating, or drinking coffee does not speed up this process. Only time reduces BAC.
Peak BAC typically occurs 30 to 70 minutes after your last drink. So your BAC may still be rising even after you stop drinking.
Does this blood alcohol calculator account for drug interactions?
No. This calculator estimates BAC based on alcohol consumption, weight, gender, and time only. It does not factor in the use of alcohol and other drugs together.
If you are taking any medication or other substances, your impairment may be significantly greater than the estimated BAC suggests. Consult a healthcare provider about how your specific medications interact with alcohol.