The Widmark formula estimates Blood Alcohol Content based on the amount of alcohol consumed, body weight, sex, and time elapsed. Results are approximate due to individual variation in alcohol metabolism.
Estimate Your BAC
How the BAC Calculator Works
This BAC calculator uses the Widmark formula, the standard method for estimating blood alcohol content from known variables: alcohol consumed, body weight, sex, and time elapsed since drinking began.
The Widmark Formula
BAC = (Alcohol in grams × 100) / (Body weight in grams × r) − (0.015 × hours). The r factor accounts for body water distribution: 0.68 for men (more muscle, less body fat) and 0.55 for women (typically higher body fat percentage). Each standard US drink contains 14 grams of alcohol.
Factors That Affect BAC
Food significantly slows alcohol absorption — eating before or during drinking keeps BAC lower and extends the time to peak. Hydration also matters. Factors like medications, liver health, age, and genetic variation in alcohol dehydrogenase enzymes affect individual metabolism, which is why calculator results can vary substantially from actual BAC.
Frequently Asked Questions
Is this BAC calculator free?
Yes, completely free with no signup required.
Is this accurate enough to use for driving decisions?
No. BAC calculators are estimates only and should NEVER be used to decide whether to drive. Individual variation in alcohol metabolism is significant (±50%). The only safe choice if you have consumed alcohol is to not drive — use a rideshare, taxi, or designate a sober driver.
What is the legal BAC limit for driving in the US?
The legal BAC limit for driving in all 50 US states is 0.08% for drivers 21 and over. Many states have lower limits for commercial drivers (0.04%) and zero-tolerance policies (0.01-0.02%) for drivers under 21. Some countries set limits at 0.05% or lower.
What is the Widmark formula?
The Widmark formula estimates BAC as: BAC = (alcohol consumed in grams) / (body weight in grams × Widmark r factor) × 100 − (elimination rate × hours). The r factor is 0.68 for men and 0.55 for women, reflecting different body water distribution. The elimination rate is typically 0.015% per hour.
How long does alcohol stay in your system?
The body eliminates alcohol at approximately 0.015% BAC per hour. A person with a BAC of 0.08% would need about 5-6 hours to reach 0.00%. Food, hydration, sleep, and individual metabolism affect this rate. Coffee, cold showers, and exercise do not speed elimination.
What counts as one standard drink?
A US standard drink contains 14 grams (0.6 oz) of pure alcohol: 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz distilled spirits (40%). Craft beers, cocktails, and wines can vary significantly from these standards.