Hi my name isXXXXX am 47 years old, slim, 173cm tall and…

Hi Sam,

Yes I am using the Widmark formula in English units (fluid ounces and pounds). The different approach I used was that I did not pool all the drinks as your explanation seemed to suggest. What I did was calculate each drink by themselves, starting with the most recent, then the next most recent and by the third most recent drink the level was basically zero, then I added them up, so only the last two drinks were considered. So the formula I used was:

BAC (%) = (A x 5.14)/(W x R) – (E – H)

A = ounces of ethanol (=drink volume in fluid ounces x percent ethanol)
W = body weight in pounds
R = distribution factor (can range from 0.6 to 0.73)
E = elimination factor (can range from 0.01 to 0.02)
H = time since started drinking in hours

This formula dose not account for all factors that are actually working in real life, such as amount of food eaten, time between drinking and eating, time it took to drink the alcohol, time it took for the stomach to empty into the intestine, and time it took to absorb into the blood from the intestines. However, you can’t look at these calculations as giving you an accurate answer. These are only estimates and can be off. This more simplified version is pretty good, it has two problem variables, that must be estimated, the distribution factor and the elimination factor. So for these two factors you can’t really know the answer for any one particular person without doing a lot of expensive and time consuming laboratory research on that one person. Plus there is day to day variation with the real values, so they must be estimated and your estimates can be wrong. Now if you try to make a more sophisticated formula that accounts for other factors, each one that you add, will also add variability and increase the chances that your answer is wrong, so adding more factors makes the estimate less reliable. There is no real solution, this will only give you an estimate, the only real measure is to actually measure your blood alcohol concentration, which you could do if you bought a breathalyzer – however they must be maintained and calibrated over time. In the U.S. and I suspect Australia as well, the BAC is not the only factor that determines if you are going to be charged with driving under the influence. Even if no BAC is determined, you can be charged if you fail field sobriety tests, or drive erratically. In fact that is how they get you for driving under the influence of drugs, as there is no such measure as a BAC for drugs. They can do a test to see if you have drugs in your blood or urine, but can’t say for sure at what concentration you are considered impaired, so they have to go off of your behavior and it usually takes a specially trained police officer to do it, called a drug recognition expert, not all police officers are drug recognition experts and can testify in court as to a persons intoxication without a BAC.

So the botXXXXX XXXXXne is that you can still be arrested for driving under the influence (in the U.S. at least) with a BAC that is under 0.08% if your behavior indicates that you are impaired, so the BAC really helps in getting a conviction, but is not as useful in getting you out of a conviction if a drug recognition expert evaluated you.

I hope this answers your question. Good luck.

Take care,
Andy