Blood Alcohol Content (BAC) Calculator
Calculate your Blood Alcohol Content (BAC) level and impairment category
How to Use
- Enter your weight in kilograms or pounds
- Select your gender (male or female)
- Enter the number of alcoholic drinks consumed
- Enter the alcohol content percentage per drink
- Enter the time period over which drinks were consumed (hours)
- Click calculate to see your BAC level and impairment category
What is Blood Alcohol Content (BAC)?
Blood Alcohol Content (BAC) is a measurement of the amount of alcohol in your bloodstream. It's expressed as a percentage, representing the grams of alcohol per 100 milliliters of blood. For example, a BAC of 0.08% means 0.08 grams of alcohol per 100ml of blood.
BAC levels are used to determine legal intoxication for driving and other activities. In most countries, a BAC of 0.08% or higher is considered legally intoxicated for operating a vehicle.
The Widmark Formula
This calculator uses the Widmark formula, a widely accepted method for estimating BAC. The formula is:
BAC = (Alcohol consumed in grams / (Body weight in grams × r)) - (0.015 × Hours)
Where 'r' is the Widmark factor: 0.68 for men and 0.55 for women. This accounts for differences in body composition and alcohol distribution between genders.
The formula also accounts for alcohol metabolism, which occurs at approximately 0.015% per hour for the average person.
BAC Levels and Impairment
| BAC Range | Category | Effects |
|---|---|---|
| 0 - 0.02% | Sober | No noticeable effects, normal behavior |
| 0.02 - 0.05% | Slight Impairment | Mild euphoria, slight relaxation, decreased inhibitions |
| 0.05 - 0.08% | Impairment | Reduced coordination, impaired judgment, decreased reaction time |
| 0.08 - 0.15% | Legally Intoxicated | Significant impairment, loss of balance, slurred speech, dangerous for driving |
| 0.15% and above | Severe Intoxication | Severe impairment, risk of alcohol poisoning, potential loss of consciousness |
Factors Affecting BAC
Many factors influence BAC levels beyond just the amount of alcohol consumed:
- Body weight: Lighter individuals reach higher BAC levels with the same amount of alcohol
- Gender: Women typically reach higher BAC levels than men of the same weight
- Food consumption: Eating before or while drinking slows alcohol absorption
- Drinking rate: Consuming alcohol quickly leads to higher BAC peaks
- Metabolism: Individual metabolism rates vary significantly
- Medications: Some medications interact with alcohol and affect BAC
- Age: Older adults may process alcohol more slowly
- Health conditions: Liver disease and other conditions affect alcohol metabolism
Legal BAC Limits
Legal BAC limits for driving vary by country and region:
- United States: 0.08% (0.00% for drivers under 21)
- United Kingdom: 0.08% in England, Wales, and Northern Ireland; 0.05% in Scotland
- Most of Europe: 0.05%
- Some countries: 0.02% or zero tolerance
- Commercial drivers often have stricter limits (typically 0.04% or lower)
Always check your local laws and remember that even below the legal limit, alcohol can impair your ability to drive safely.
Alcohol Safety Tips
- Never drink and drive - use designated drivers, taxis, or rideshare services
- Know your limits and drink responsibly
- Eat food before and while drinking to slow alcohol absorption
- Alternate alcoholic drinks with water to stay hydrated
- Avoid mixing alcohol with medications or other substances
- Be aware that tolerance does not mean reduced impairment
- Look out for friends who may have had too much to drink
- Call emergency services if someone shows signs of alcohol poisoning
- Remember that only time eliminates alcohol from your system - coffee, cold showers, and exercise don't work
Frequently Asked Questions
- How accurate is this BAC calculator?
- This calculator provides estimates based on the Widmark formula, which is widely used but not 100% accurate. Individual BAC levels can vary significantly based on metabolism, food consumption, medications, and other factors. The only way to know your exact BAC is through a breathalyzer or blood test. Always err on the side of caution.
- What is considered a standard drink?
- A standard drink contains approximately 14 grams of pure alcohol. This equals about 12 oz (355ml) of beer at 5% alcohol, 5 oz (148ml) of wine at 12% alcohol, or 1.5 oz (44ml) of distilled spirits at 40% alcohol. The calculator adjusts for different alcohol content percentages.
- How long does it take for BAC to return to zero?
- The average person metabolizes alcohol at approximately 0.015% per hour. However, this rate varies significantly between individuals. Generally, it takes about one hour per standard drink to fully metabolize the alcohol, but this is just an estimate. The calculator provides an estimated time until sober based on the average metabolism rate.
- Can I speed up alcohol metabolism?
- No. Only time eliminates alcohol from your system. Coffee, cold showers, exercise, or other remedies do not speed up alcohol metabolism. The liver processes alcohol at a constant rate that cannot be accelerated. The only safe option is to wait until your body has metabolized the alcohol naturally.
- Is it safe to drive at BAC levels below the legal limit?
- Even at BAC levels below the legal limit, alcohol impairs judgment, coordination, and reaction time. Some impairment can occur at levels as low as 0.02%. The safest choice is not to drive after consuming any alcohol. Legal limits are maximum thresholds, not safe drinking guidelines for driving.