Blood Alcohol Concentration (BAC) Calculator
Enter your gender, weight, number of drinks, and time elapsed to estimate your Blood Alcohol Concentration (BAC) using the Widmark formula.
Important Disclaimer
This tool is for educational and reference purposes only. Actual BAC may differ significantly from estimates. Never use this to determine whether it is safe to drive or operate machinery. If you have been drinking, use a designated driver or public transportation.
How to Use
- Select your gender (male or female), which affects the Widmark r factor.
- Enter your weight in kilograms (kg).
- Enter the number of standard drinks you have consumed.
- Enter the number of hours since you started drinking.
- Click "Estimate BAC" to see your estimated BAC and status level.
Widmark Formula Explained
BAC(%) = (Alcohol(g) / (Body Weight(kg) × r × 10)) - (0.015 × Time(h))r factor: Male = 0.68, Female = 0.55 (Widmark body water distribution constant)
1 standard drink = 14 grams of pure alcohol
0.015 = average BAC (%) metabolized per hour
BAC Levels and Effects
| BAC Range | Status | Typical Effects |
|---|---|---|
| 0.00% | Sober | No alcohol effects |
| 0.01-0.03% | Minimal | Slight relaxation, barely noticeable effects |
| 0.03-0.05% | Mild Effects | Relaxed mood, increased sociability, slight impairment of judgment |
| 0.05-0.08% | Impaired Judgment | Slower reactions, reduced coordination, noticeably impaired judgment |
| 0.08-0.15% | Legally Intoxicated | Severe coordination difficulties, blurred vision, greatly increased reaction time |
| 0.15%+ | Severely Intoxicated | Confusion, possible vomiting, risk of life-threatening complications |
Calculation Example
Given: Male, 70 kg, 3 standard drinks, 1 hour elapsed
Step 1: Alcohol = 3 × 14 = 42g, Weight = 70kg, r = 0.68
Step 2: BAC = (42 / (70 × 0.68 × 10)) - (0.015 × 1) = (42 / 476) - 0.015 = 0.0882 - 0.015 = 0.0732
Result: BAC is approximately 0.0732%, classified as "Impaired Judgment", approaching the legal DUI threshold.
Important Notes
- Estimate Only: This tool uses a simplified Widmark formula. Actual BAC is affected by many personal factors (body fat percentage, empty/full stomach, liver function, etc.) and may differ significantly from the estimate.
- Legal Standards: The legal DUI limit varies by country. In many US states, 0.08% is the legal limit. In Taiwan, the limit is 0.03% BAC. Always check your local laws.
- Individual Differences: For the same amount of alcohol, people with lower body weight, females, those on an empty stomach, or those with reduced liver function will typically have higher BAC levels.
- Drug Interactions: Certain medications (such as sedatives, antihistamines) can amplify alcohol effects. Even at low BAC levels, judgment and reaction ability may be severely impaired.
- Safety First: If you have had any alcohol, regardless of your estimated BAC, it is recommended to use a designated driver, taxi, or public transportation instead of driving.
- This tool is for educational and reference purposes only and cannot replace professional medical or legal judgment. If in doubt, consult a physician or legal professional.
Frequently Asked Questions
What is BAC (Blood Alcohol Concentration)?
BAC (Blood Alcohol Concentration) is the percentage of alcohol in your bloodstream. For example, a BAC of 0.08% means there is 0.08 ml of pure alcohol per 100 ml of blood. BAC is a key metric for measuring alcohol's effects on the body and is the legal standard for DUI/DWI in most countries.
What is a "standard drink"? How many standard drinks is one beer?
A standard drink contains approximately 14 grams of pure alcohol. One 350ml can of 5% beer equals about 1 standard drink; one 150ml glass of 12% wine equals about 1 standard drink; one 45ml shot of 40% spirits (whiskey, vodka, etc.) equals about 1 standard drink. Cocktails and craft beers may contain more alcohol, so take care.
How accurate is the Widmark formula? What are its limitations?
The Widmark formula is the most widely used BAC estimation method, but it is a simplified model. Actual BAC is also influenced by: drinking speed (binge drinking leads to higher BAC), empty stomach (faster absorption), body fat percentage (fat does not absorb alcohol), individual metabolic rate differences, age and health. Therefore, results are estimates only and should never be used to determine safe driving ability.
How long after drinking can I drive?
The body metabolizes approximately 0.015% BAC per hour on average. For a BAC of 0.08%, it would theoretically take about 5-6 hours to fully metabolize. However, individual variation is significant — if you drank heavily the night before, you may still be over the limit the next morning. The safest approach is to wait a sufficient amount of time and confirm you are completely sober before driving. The best practice is simply not to drive on the day you drink.