BAC Calculator (Blood Alcohol)
Estimate your Blood Alcohol Concentration (BAC) using the Widmark formula. Enter your gender, body weight, number of standard drinks, and hours since your first drink.
About Blood Alcohol Concentration
Blood Alcohol Concentration (BAC) measures the amount of alcohol in your bloodstream as a percentage. It is affected by factors including body weight, gender, the amount and type of alcohol consumed, and time elapsed since drinking. This calculator uses the Widmark formula, the most widely accepted method for estimating BAC.
The Widmark Formula
BAC = (Alcohol consumed in grams x 0.806) / (Body weight in kg x r) - (0.015 x hours since first drink). The gender constant (r) is 0.68 for men and 0.55 for women, reflecting differences in body water content. The 0.015 hourly elimination rate is the average for most adults.
Standard Drink Equivalents
- Regular beer (5%): 12 oz / 355 ml
- Craft/IPA beer (7-9%): counts as 1.4 - 1.8 standard drinks per 12 oz
- Wine (12%): 5 oz / 148 ml
- Spirits (40%): 1.5 oz / 44 ml
- Each standard drink equals approximately 14 grams of pure alcohol
BAC Levels and Effects
- 0.02%: Slight mood changes, relaxation, mild warmth
- 0.05%: Lowered inhibitions, impaired judgment, reduced alertness
- 0.08%: Legal limit in most US states — impaired coordination and reaction time
- 0.10%: Clear deterioration of motor control, slurred speech
- 0.15%: Significant impairment, possible vomiting, difficulty walking
- 0.20%: Confusion, disorientation, need for assistance
- 0.30%+: Risk of loss of consciousness, alcohol poisoning — medical emergency
Factors That Affect BAC
- Body weight and composition — more body water dilutes alcohol more effectively
- Biological sex — women generally reach higher BAC than men of the same weight
- Food in the stomach — eating slows absorption and lowers peak BAC
- Rate of consumption — drinking faster leads to higher peak BAC
- Medications — many drugs interact with alcohol and can intensify impairment
- Hydration level — dehydration can increase the effects of alcohol
US DUI/DWI Legal Limits
- Most states (49 of 50): 0.08% BAC for drivers 21+
- Utah: 0.05% BAC (lowest in the nation since 2018)
- Commercial drivers: 0.04% BAC nationwide
- Under 21: Zero tolerance (0.00% - 0.02% depending on state)
Disclaimer: This calculator provides estimates only. Actual BAC varies based on many factors including metabolism, food intake, medication, and individual tolerance. Never rely on a calculator to determine if you are safe to drive. When in doubt, do not drive. If you or someone you know may have alcohol poisoning, call 911 immediately.