The Injustice of the 2100 Blood/Breath Conversion Factor

Posted On December 26, 2023 Charles Ramsay

As a DWI defense attorney, I've seen countless cases where the guilt or innocence of a person accused of a DWI hinges on a single number coming from a breath machine. These devices, while commonly used, are far from infallible. A major problem with them is that they rely on a constant blood/breath conversion factor of 2100. 

The state breath machines are calibrated to estimate your blood alcohol concentration. They do this using an assumed conversion factor of 2100. The conversion factor assumes that there’s the same amount of alcohol in 1 part of blood as in 2100 parts of breath.

But like everything dealing with the human body, there’s a lot of individual variation. Our bodies are not all the same. Factors like weight, gender, metabolism, and even recent food intake can significantly impact how breathalyzers read BAC. A 2100 conversion factor ignores these crucial individual differences, leading to inaccurate and unfair readings.

The conversion factor can vary wildly. A study by A.W. Jones showed that the conversion factor can be off by more than 200%! Take a look at the ranges in the image below. When breath was sampled 30 minutes after drinking, some had a conversion factor of 990.

So, a person whose conversion factor was only 990 would’ve had their blood alcohol overestimated by 212%.

Here’s to determine how different conversion factors affect your estimated alcohol level.

Suppose the machine printed out a 0.09 for your estimated alcohol level. It is very possible that your individual conversion factor is closer to 1700 (not 2100). 

To figure out your new estimate, you’d take 0.09 / 2100 * 1700 = 0.073.


The breath machine overestimates actual alcohol levels 14 -35% of the time (depending on the study). Look at the graph showing the normal bell curve of the blood/breath conversion factor. That doesn’t look like sound science to me.


If shoddy estimates of your alcohol level have victimized you, call Ramsay Law. We know the science, and we know the law. We stay updated with the latest research to keep the state in check.

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