What this tool does
This calculator uses body weight, U.S. standard drinks, and hours since the first drink to produce a simplified blood alcohol concentration (BAC) estimate. It is an educational model for comparing assumptions, not a breath or blood test, medical assessment, or decision tool for driving and other safety-critical activities.
How to use it
- Select the body-profile coefficient used by the formula and enter weight in kilograms. The two profile choices cannot represent every biological or individual difference.
- Enter the number of U.S. standard drinks and the grams of pure alcohol per drink. The default is 14 g, but a large or strong serving can contain more than one standard drink.
- Enter hours since the first drink, calculate, and read the warning with the estimate. Never use a low or zero result as permission to drive, operate equipment, swim alone, or take another risk.
Calculation method
Pure alcohol＝drinks×grams per drink. Initial estimated BAC (%)＝pure alcohol g÷(weight kg×1,000×distribution coefficient)×100, using 0.68 for the male profile and 0.55 for the female profile. Displayed estimate＝max(0, initial estimate−0.015×elapsed hours). This is a simplified Widmark-style model with a fixed linear elimination assumption; it does not measure absorption or metabolism.
Worked example
For the male profile, 70 kg, two default U.S. standard drinks, and two hours since the first drink, pure alcohol is 28 g. The model gives about 0.0588% before the time adjustment and subtracts 0.0300 percentage points, displaying about 0.0288%. That number is not a measured BAC and does not mean the person is safe to drive.
Common uses
- Learning how U.S. standard drinks relate to grams of pure alcohol
- Comparing how weight and elapsed-time assumptions change this model
- Reviewing a serving by alcohol content instead of counting glasses or containers
Limitations and safety
Actual BAC varies with drinking speed, food, body water, age, health, medications, liver function, serving size, alcohol strength, and individual metabolism. BAC may continue rising after the last drink, and only time lowers alcohol in the body; coffee, showers, food, or exercise do not make someone sober. Do not drive after drinking. If someone is difficult to wake, confused, vomiting repeatedly, having a seizure, breathing slowly or irregularly, or has pale, blue, cold, or clammy skin, contact local emergency services immediately and do not leave the person alone.
Frequently asked questions
Does one drink mean one beer, glass, or shot?
Not necessarily. A U.S. standard drink contains about 14 g of pure alcohol. Container size and alcohol by volume determine how many standard drinks a serving contains.
Can I drive if the estimate is zero?
No. Inputs may be incomplete, metabolism differs, and the result is not a measurement. If you have been drinking, choose a sober driver, public transit, taxi, or another safe option.