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Free online BAC calculator

BAC measures the concentration of alcohol in your blood as a percentage. This calculator uses the Widmark formula to estimate BAC from standard drinks, body weight, and time.

1 drink = 12 oz beer / 5 oz wine / 1.5 oz spirits

About this calculator

How to use

  1. Enter the number of standard drinks consumed.
  2. Enter your body weight in pounds.
  3. Enter hours since your first drink.
  4. Select your biological sex (affects the Widmark factor).
  5. Click Calculate BAC.

Note: This is an educational tool only. Never use it to decide whether to drive. Only a breathalyzer or blood test gives an accurate BAC reading.

Formula

BAC = (A × 5.14 / (W × r)) − (0.015 × H)

VariableMeaning
AStandard drinks consumed
WBody weight in pounds
rWidmark factor (0.73 male / 0.66 female)
HHours since first drink
0.015Alcohol elimination rate (%/hour)

Worked example

160 lb male, 3 drinks, 1 hour elapsed:

BAC = (3 × 5.14) / (160 × 0.73) − (0.015 × 1) = 15.42 / 116.8 − 0.015 ≈ 0.117%

Hours to sober = 0.117 / 0.015 ≈ 7.8 hours

Frequently asked

How is BAC calculated?
The Widmark formula: BAC = (drinks × 5.14 / (weight_lbs × r)) - (0.015 × hours). The Widmark factor r is 0.73 for males and 0.66 for females, reflecting differences in body water content. The 0.015 is the average elimination rate per hour.
What is a standard drink?
In the United States, a standard drink contains 14 grams (0.6 oz) of pure alcohol — equivalent to 12 oz of regular beer (5%), 5 oz of wine (12%), or 1.5 oz of distilled spirits (40%). Different countries define standard drinks differently.
Why is the result an estimate?
Actual BAC varies based on food consumed, hydration, medications, liver function, body composition, and individual metabolism. The Widmark formula gives an average estimate, not a precise measurement. Only a breathalyzer or blood test provides an accurate BAC.
What is the US legal driving limit?
The legal blood alcohol concentration limit for driving in the US is 0.08% (80 mg/dL) for adults 21 and over. Commercial drivers are held to 0.04%. Any amount of alcohol impairs driving — never drink and drive.
How long until I am sober?
The liver metabolizes alcohol at roughly 0.015% BAC per hour on average. To estimate hours until sober, divide your current BAC by 0.015. Coffee, cold showers, and food do not speed up elimination.

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