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How does a BAC Calculator work?

Every single BAC calculator operates in a similar way. They take some input values (height, weight, age, biological sex, drinks consumed, and time spent drinking), and then they perform some simple calculations.

The calculations used can differ, but most BAC calculators use some variation of the Widmark formula. The Widmark formula was devised in the 1930's by Erik Widmark, and is still considered to be one of the best ways to estimate a person's blood alcohol content.

How does Drunk Calc work?

Drunk Calc uses an advanced algorithm to determine your BAC based on as little information as possible. Our BAC calculator only needs to know your weight, height, biological sex, the drinks you've consumed, the amount of food you've eaten, and the amount of time you've been drinking.

Drunk Calc's algorithm is based on the Widmark formula. However, while other blood alcohol calculators often use the Widmark formula in its entirety, Drunk Calc has taken it and improved it to achieve a higher level of accuracy.

Our Advanced BAC Calculator Algorithm

This is our advanced BAC calculator algorithm:

BAC = (A / r * W) * 100 - B * t

  • BAC is the blood alcohol level (%)
  • A is the mass of alcohol absorbed (grams)
  • r is the Widmark factor
  • W is the mass of the individual (grams)
  • B is the alcohol elimination rate (assumed constant at 0.015% per hour)
  • t is the time that has elapsed since drinking began (hours)

The algorithm itself is nothing new, but there are two main areas where the Drunk Calc algorithm outshines the competition. First, Drunk Calc uses a new and improved Widmark factor, and second, Drunk Calc uses your hunger level to determine how much alcohol has been absorbed at any given time.

The new and improved Widmark factor was first proposed by Posey and Mozayani in the journal article "The estimation of blood alcohol concentration: Widmark revisited", published in 2007. In the journal article they outline a more comprehensive method of obtaining the factor, which in turn gives a more accurate BAC without needing to know your age. You can click here to read all about the updated Widmark factor.

The problem with most BAC calculators is that they assume full alcohol absorption has occurred the moment the drink is consumed. In reality, it can take anywhere from 30 minutes to 2 hours for the alcohol in a drink to be fully absorbed by the body.

To account for the absorption rate of alcohol, Drunk Calc will ask you how hungry you were when you had each drink. This data is then used to estimate how quickly the alcohol has been absorbed, which then gives a more accurate blood alcohol calculation.

Alcohol Absorption Algorithm

The algorithm used to determine the amount of alcohol absorbed is:

Y = 100 - 100 / (2 ^ (X / Z))

  • Y is the amount of alcohol that has been absorbed from a specific drink (%)
  • X is the time that has passed since the drink was consumed (minutes)
  • Z is the time required for half of the drink's alcohol to be absorbed (minutes)

Z, the half-life of the alcohol absorption, was determined with the help of a journal article titled "Pharmacokinetics of Ethanol - Issues of Forensic Importance", which was published by Alan Wayne Jones in 2011. The journal outlines the "starving" and "full" rates of alcohol absorption, as well as the half-lives of each. You can click here to learn more about the absorption of alcohol.