πΊ BAC Calculator
Blood alcohol content estimate using the Widmark formula.
For informational purposes only, not medical advice. Consult a healthcare professional.
How the BAC Calculator Works
This calculator uses the Widmark formula, the standard method researchers and courts use to estimate blood alcohol concentration. A standard drink in the United States is defined as 14 grams of pure alcohol: one 12-ounce beer at 5 percent, one 5-ounce glass of wine at 12 percent, or one 1.5-ounce shot of 80-proof spirits. Enter your weight, the number of standard drinks, your sex, and the hours since you started drinking, and the calculator estimates your current BAC along with the impairment level you can expect at that range.
The formula is BAC = (alcohol grams / (body weight in grams x r)) x 100 minus 0.015 per hour of metabolism, where r is 0.68 for men and 0.55 for women. That r value reflects average body water percentage, which is why weight and sex matter so much: two people can drink the same amount and end up with very different BACs. The 0.015 per hour is the average rate the liver clears alcohol, though real rates vary from about 0.010 to 0.025.
Reading Your Result
In every US state the legal driving limit is 0.08 percent. Impairment starts well below that: at 0.02 to 0.03 you feel relaxed and judgment is already softening, at 0.05 coordination and reaction time are measurably worse, at 0.08 memory and reasoning are impaired, and at 0.15 and above you risk blackouts, vomiting, and alcohol poisoning. The calculator labels your estimated range so you can see where you fall. Remember that this is an estimate, not a breathalyzer: food, medications, fatigue, and individual metabolism all shift the real number.
Worked Example
A 170-pound man drinks 4 standard beers over 3 hours. Alcohol grams = 4 x 14 = 56. Body weight in grams = 170 x 453.6 = 77,112. Raw BAC = (56 / (77,112 x 0.68)) x 100 = 0.107. Subtract metabolism: 3 hours x 0.015 = 0.045. Estimated BAC = 0.062 percent, below the legal limit but impaired enough that driving is unsafe. A 130-pound woman drinking the same amount: raw = (56 / (58,968 x 0.55)) x 100 = 0.173, minus 0.045 = 0.128, well over the limit. Same drinks, very different result.
Staying Safe
The only BAC that is safe for driving is 0.00. Plan your ride home before the first drink, pace yourself at no more than one standard drink per hour, alternate with water, and eat beforehand. If you feel buzzed, you are already impaired. This tool is for education and planning, never for deciding you are okay to drive. For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
How accurate is a BAC calculator?
It is an estimate, not a measurement. The Widmark formula uses averages for body water and metabolism, but real BAC varies with food, medications, fatigue, hydration, and individual liver function. Treat the number as a planning guide. A breathalyzer or blood test is the only way to know your actual BAC.
What counts as one standard drink?
In the US, one standard drink is 14 grams of pure alcohol: 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 80-proof spirits. Craft beers, large wine pours, and mixed drinks often contain 1.5 to 3 standard drinks, so count carefully or you will underestimate.
How long does it take to sober up?
The liver clears roughly 0.015 BAC per hour on average. From 0.12 it takes about 8 hours to reach zero. Coffee, cold air, exercise, and food do not speed this up. Only time works.
Why do women reach higher BAC than men?
Women average a lower percentage of body water (the r factor is 0.55 vs 0.68 for men), so the same alcohol is dissolved in less water, producing a higher concentration. Weight matters too: lighter people of either sex reach higher BACs.
Can I drive at 0.07?
No. Impairment begins around 0.02, and at 0.05 to 0.07 reaction time, coordination, and judgment are already degraded. The 0.08 limit is a legal line, not a safety line. The only safe BAC for driving is zero.