BAC Calculator
This Blood Alcohol Content (BAC) calculator uses the Widmark formula to provide a rough estimate of your current BAC based on your weight, sex, number of drinks, and time elapsed. IMPORTANT: This tool provides estimates only and should never be used to determine whether it is safe to drive or operate machinery. Alcohol affects every individual differently. Never drive after drinking — always arrange a safe ride home.
Quick Answer
One standard drink raises BAC by roughly 0.02–0.03%. The legal driving limit in most U.S. states is 0.08%.
These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.
How the Formula Works
Determine the total ounces of pure alcohol consumed. A standard drink contains approximately 0.6 oz of pure alcohol.
alcohol (oz) = numberOfDrinks x 0.6Identify the Widmark factor (r) based on biological sex: 0.73 for males, 0.66 for females.
r = 0.73 (male) or 0.66 (female)Apply the Widmark formula to estimate BAC before accounting for time.
raw BAC = (alcohol_oz x 5.14) / (weight_lbs x r)Subtract the metabolism rate multiplied by hours since first drink. The body metabolizes alcohol at approximately 0.015 BAC per hour.
BAC = raw BAC - (0.015 x hours)If the result is negative, BAC is set to 0.00 (the body has fully metabolized the alcohol).
BAC = max(0, BAC)
How to Interpret Your Results
BAC values indicate the concentration of alcohol in your bloodstream. Even low BAC levels can impair judgment and reaction time. The legal driving limit in most US states is 0.08, but impairment begins well before that threshold. These categories are general guidelines only.
- Sober
- 0–0 — No measurable blood alcohol content.
- Minimal Effects
- 0.01–0.03 — Slight mood elevation. Most people feel minimal effects.
- Relaxation, Mild Impairment
- 0.04–0.07 — Lowered inhibitions, mild euphoria. Judgment and fine motor skills begin to be affected.
- Legally Impaired
- 0.08–0.14 — At or above the legal limit. Significant impairment of motor coordination, judgment, and reaction time.
- Significant Impairment
- 0.15–1 — Severe impairment of all mental and physical functions. Risk of loss of consciousness.
Limitations
- BAC estimates are based on the Widmark formula, which uses population averages and cannot account for individual physiological differences such as enzyme levels, liver function, or genetics.
- Food intake, hydration, medications, and overall health significantly affect how alcohol is absorbed and metabolized, but are not factored into this estimate.
- This calculator assumes standard drink sizes (12 oz beer at 5% ABV, 5 oz wine at 12% ABV, 1.5 oz spirit at 40% ABV). Actual drink sizes and alcohol content vary widely.
- The Widmark factor uses average body water ratios for males and females, which may not reflect your individual body composition.
- This tool should never be used to determine whether it is safe to drive or operate machinery. The only safe amount of alcohol before driving is zero.
Frequently Asked Questions
How accurate is a BAC calculator?
What is the legal BAC limit for driving?
How long does it take for alcohol to leave my system?
What is a standard drink?
Why does BAC differ between males and females?
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