BAC Calculator - Blood Alcohol Content
Use this Blood Alcohol Content (BAC) calculator to estimate your blood alcohol level based on the number of drinks you've had, your body weight, gender, and time elapsed. Understand your impairment level and know when it's safe to drive.
How to Use
- Select the number of drinks you have consumed (1-10 standard drinks).
- Choose the drink type — beer, wine, or spirits. Each counts as one standard drink (~14g alcohol).
- Enter your body weight and select pounds or kilograms.
- Select your gender — Male or Female (affects the Widmark factor).
- Enter hours since your first drink to account for alcohol metabolism.
- Click "Calculate BAC" to see your estimated blood alcohol content and interpretation.
Formula / Method
Widmark Formula:
BAC = (A / (W × r)) - (0.015 × t)
Where:
- A = Total alcohol consumed (grams)
- W = Body weight (grams)
- r = Widmark distribution factor: 0.68 (male), 0.55 (female)
- t = Hours since first drink
- 0.015 = Average alcohol elimination rate per hour (g/dL)
One standard drink (US) = 14 grams of pure alcohol. This calculator uses the Widmark equation, the most widely accepted method for estimating BAC.
BAC Level Reference Chart
| BAC Range | Impairment Level | Effects |
|---|---|---|
| 0.00 - 0.02% | Sober / Minimal | No noticeable effects; behavior normal. |
| 0.03 - 0.05% | Buzzed / Mild | Relaxation, slight euphoria, lowered inhibitions. |
| 0.06 - 0.07% | Moderate | Impaired judgment, reduced coordination, slowed reaction time. |
| 0.08 - 0.14% | Legally Impaired | Legal limit in most US states. Significant impairment of motor skills. |
| 0.15 - 0.29% | Severely Impaired | Risk of blackout, blurred vision, loss of balance, nausea. |
| 0.30%+ | Life-Threatening | Risk of alcohol poisoning, unconsciousness, respiratory depression. |
Examples
A 180 lb (81.6 kg) male consumes 4 standard drinks (56 g alcohol) over 2 hours. Using the Widmark formula: BAC = (56 / (81600 × 0.68)) - (0.015 × 2) = 0.100% - 0.03% = 0.070%. This is below the 0.08% legal limit, but still shows moderate impairment. It would take approximately 4.7 more hours to reach zero BAC.
Frequently Asked Questions
How long does alcohol stay in your system?
Alcohol is metabolized at an average rate of about 0.015% BAC per hour. For a typical person, it takes roughly 1-2 hours to eliminate one standard drink. However, this varies based on weight, gender, age, liver function, and food consumption. A BAC of 0.08% (legal limit) takes about 5-6 hours to reach zero. Alcohol can be detected in blood for up to 12 hours, in breath for 24 hours, and in urine for 12-72 hours depending on the test method.
What is the legal BAC limit?
In the United States, the legal BAC limit for driving is 0.08% (0.08 g/dL) for adults aged 21 and over. For commercial drivers, the limit is 0.04%. Drivers under 21 are subject to "zero tolerance" laws, typically 0.01-0.02% depending on the state. Many other countries have stricter limits: 0.05% in most of Europe, Australia, and New Zealand, and 0.02% in Sweden and Norway. Penalties for DUI/DWI include fines, license suspension, and even jail time.
Does food affect BAC?
Yes, consuming food before or while drinking significantly affects BAC. Food slows gastric emptying and delays alcohol absorption into the bloodstream, resulting in a lower peak BAC. A full stomach can reduce peak BAC by up to 30-50% compared to drinking on an empty stomach. Fatty and protein-rich foods are especially effective at slowing absorption. However, food does not speed up alcohol metabolism — once alcohol is absorbed, it is eliminated at the same rate regardless of food intake.
How accurate is this BAC calculator?
This calculator provides an estimate based on the Widmark formula. Actual BAC depends on many individual factors including metabolism, liver health, hydration level, food intake, medications, and genetics. The calculator should be used for educational purposes only and should not be used to determine whether it is safe to drive. When in doubt, do not drive after consuming alcohol.