BAC Calculator

What is the BAC Calculator?

BAC stands for Blood Alcohol Concentration — the percentage of alcohol in your bloodstream at any given time. This calculator estimates your BAC based on how much you've drunk, your body weight, your sex, and how long you've been drinking. It's a tool for understanding how alcohol moves through the body and how slowly it leaves. For reference, the legal driving limit is 0.08% in most US states (Utah is 0.05%), but no estimate can tell you whether you are fit to drive. Only time makes you sober, and if you've been drinking, don't drive. CalciHub's version gives you an estimate, not a breathalyzer reading — but the formula is medically established.

How Does It Work?

The Widmark Formula is the standard method used in forensic and medical contexts to estimate BAC. It accounts for your weight, body composition (which differs by sex), and how much alcohol has already metabolized out of your system since you started drinking.

BAC = (Alcohol Consumed in grams / (Weight in grams x r)) x 100 - (0.015 x Hours)

Alcohol in grams = Number of drinks x 14 (one standard US drink = 14g pure alcohol)

r = body water constant: 0.55 for women, 0.68 for men

0.015 = average BAC metabolized per hour

Hours = time elapsed since you started drinking

How to Use CalciHub's BAC Calculator

1. Enter your body weight and select the unit (lbs or kg).

2. Select your biological sex (this affects the Widmark constant).

3. Enter the number of standard drinks consumed.

4. Input how many hours have passed since you started drinking.

5. Click Calculate — your estimated BAC appears alongside an impairment label and an estimate of how many hours until it returns to zero.

Tip: One 'standard drink' is 12oz regular beer, 5oz wine, or 1.5oz spirits. Mixed drinks often contain more than one standard drink — factor that in when counting.

A Quick Example

Mike, 180 lbs, has had 3 beers over 2 hours at a backyard party in Denver.

Inputs: Weight = 180 lbs (81.6 kg), Sex = Male, Drinks = 3 standard drinks, Hours = 2

Alcohol in grams = 3 x 14 = 42g

BAC = (42 / (81,600 x 0.68)) x 100 - (0.015 x 2) = 0.076 - 0.030 = 0.046%

Result: Estimated BAC = 0.046%, with roughly 3 hours before it returns to zero.

What the number really shows is how slowly alcohol clears: three drinks are still measurably in Mike's system two hours later, and only time changes that. Nothing about this estimate makes it safe to drive — the calculator exists to make the metabolism visible, not to clear anyone to get behind the wheel.

Frequently Asked Questions