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 355 mL (12 oz) servings consumed
- Enter the ABV for each 355 mL (12 oz) serving
- 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 thresholds are used in some jurisdictions when assessing driving offenses, but the legal limit depends on local law, driver category, and circumstances. This estimate cannot determine legal status or whether driving is lawful.
The Widmark Formula
This calculator uses the Widmark formula, a widely accepted method for estimating BAC. The formula is:
BAC fraction = (Alcohol consumed in grams / (Body weight in grams × r)) - (0.00015 × Hours); multiply by 100 to display percent
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% | Estimated low range | Effects vary; the estimate cannot establish absence of impairment |
| 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% | Range used by some legal thresholds | Impairment may be substantial; do not use this estimate to determine legality or driving safety |
| 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:
- Examples only: United States: 0.08% (0.00% for drivers under 21)
- Examples only: United Kingdom: 0.08% in England, Wales, and Northern Ireland; 0.05% in Scotland
- Examples only: Most of Europe: 0.05%
- Examples only: Some countries: 0.02% or zero tolerance
- Driver-specific rules may be stricter, including for commercial drivers
Check the current official rules where you are and for your driver category. A legal threshold is not a safety threshold, and this estimate cannot prove sobriety, legality, or fitness to drive.
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 does one entered serving mean?
- Each serving entered is exactly 355 mL (12 oz) at the ABV you provide. It is a fixed-volume input, not a generic standard drink. Convert other beverage sizes into equivalent 355 mL servings before using the calculator.
- How long does it take for BAC to return to zero?
- The formula subtracts approximately 0.015 percentage points per hour, but actual rates vary significantly. The displayed time is only an estimate to a calculated BAC of 0%; it does not establish sobriety or driving safety.
- 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. Actual rates vary, so do not use this estimate to decide when it is safe or legal to drive.
- Does a BAC estimate below the local legal limit prove that driving is safe?
- No. Legal limits vary by jurisdiction and driver category, and a calculated value is not a measurement or proof of sobriety, legality, or driving safety. Alcohol can impair judgment, coordination, and reaction time below legal thresholds; the safest choice is not to drive after drinking.