DUI & Blood Alcohol – How Much is Too Much?

In previous articles we’ve gone over the two ways that the police and prosecutors use measurements of blood alcohol concentration (BAC) to prove a DUI charge. One is the well-known “over the limit” Unlawful Blood Alcohol law which makes it illegal to be in control of a vehicle while your blood contains .08% or more of alcohol. The other is through the presumption of impairment of normal faculties which the law provides for anyone whose BAC is .08% or more. Because the police and prosecutors rely heavily upon BAC measurements, it would be helpful to be able to supplement your self-evaluation of your condition of impairment for driving by being able to estimate in some way the point at which your drinking has reached the legal limit. Thus it is extremely important to understand how the amount that you drink and the timing of any drinks you have consumed are related to your blood alcohol level and your ability to drive safely and legally.

Don’t Leave Without Your Normal Faculties

Even though the police and the prosecutor may rely heavily on BAC measurement results, as taken by either a breath-test or a blood-draw, you should not use that as your only, or even your most important standard for making a decision whether or not to drive! Remember that what is really important for operating a vehicle is not some number from a machine, but your reaction time, coordination and ability to think clearly. These attributes are referred to as “normal faculties” in Florida DUI law. You may not and should not operate a vehicle if you have drunk alcohol to the extent that your normal faculties are impaired. The law defines normal faculties as “the ability to see, to hear, to walk, to talk, to judge distances, to drive, to make judgments, to act in emergencies and to normally perform the many mental and physical tasks of daily life.”

Before making the decision whether or not to drive, you must decide whether you are impaired from alcohol. You can ask others, hopefully sober themselves, for their opinion or you can make your own self assessment of your coordination and balance. Probably the best thing to keep in mind in deciding whether you are impaired from alcohol is to remember one wise rule: If you feel buzzed you shouldn’t drive! In other words, if you know that you are feeling the effects of your drinks, then regardless of what you think your BAC may be, you should not attempt to drive. However, even if you believe you feel fine, you may like to know if the numbers of drinks you have had have put your BAC over the legal limit.

Remember in School When They Said Math Would Be Important Some Day?

A mathematical formula which is very important to DUI cases is used to calculate the blood alcohol concentration which results from a given amount of alcohol drank over a known period of time by a person. Like most mathematical equations, it can be used in reverse to calculate an estimate of the number of drinks someone must have consumed in order to achieve a particular BAC. This formula has developed over the past century and has been modified over time to reflect better understanding of how the human body absorbs and eliminates alcohol.

The most widely used variation of this formula is called “Widmark’s Formula” after the Swedish scientist who initially developed it in the 1930’s:

C [mg/g] = A/(p [kg] x r).

In other words, the blood alcohol concentration (C) equals the amount of pure alcohol drank divided by the drinker’s weight (in kilograms) multiplied by the percent of body weight which is not bone or fat. In order to arrive at a BAC for a period of time after the alcohol had been consumed, it is necessary to subtract the amount of alcohol which is eliminated from the body over that period of time. Modern versions of Widmark’s formula also take into account other physiological factors, as well as trying to individualize the formula for different age, gender and body types.

As bad as sitting at a bar attempting to calculate your BAC from that equation may be, it is even worse when you consider that you would also have to calculate the amount of pure alcohol present in whatever your beverage(s) of choice had been. And the arithmetic doesn’t get any easier as you keep drinking!

O.K., Enough Math – Where’s the Short-Cut?

Even the most modern version of this equation makes assumptions about a person’s body and alcohol absorption and elimination rates which are average estimates. Therefore, it is highly unlikely that any calculation of BAC based upon the number of drinks consumed would be exactly accurate for your body or any other individual. However, it is possible to remember a simple rule which would give you an idea of where your BAC could stand in relation to the Florida legal limit of .08% BAC. A conservative estimate of where your drinking has put your blood alcohol level requires that you be able to accurately keep track of two things: the number of drinks you have had; and the number of complete hours that have passed since you started drinking (these must all be hours in which at least one drink was consumed – if you start drinking in the morning and then stop and later start drinking that night, no fair counting the hours in between!).

In order to count your drinks it is very important that you be accurate. One drink would equal a 12 ounce American beer, a drink made with an ounce and a half of 80 proof liquor, or 4 ounces of non-fortified wine. If you drink imported beer, 180 proof liquor or other drink stronger than those mentioned above, you must count each drink as two drinks. In addition, if you suspect that the bartender is pouring extra strong drinks for you (very common in bars where you get to know the staff) you need to count each drink as two drinks.

When you want to see if your BAC is near the legal limit, you should total up the number of full hours since you started drinking (and never stopped). Don’t count forty-five minutes as an hour, this needs to be full hours. Also, this calculation assumes that you began drinking with a zero BAC. So, you cannot use this simplified method if you already had alcohol in your body before you “started drinking”. Since alcohol is continuously being eliminated from your body by being metabolized and by leaving through your breath and urine on average rate of about equal to the amount of alcohol in one standard drink per hour, you can subtract the total hours since you started drinking from your total number of drinks. The result will be the approximate number of drinks worth of alcohol that remain in your body. From the number that remains you can get a conservative idea whether you would be close to the legal limit based upon the following:

Conservative Estimate of Drinks Remaining In Body to Reach Legal Limit – .08%

Weight Female Male
100 pounds 1 ½ drinks remaining N/A
125 – 140 pounds 2 drinks remaining N/A
150 – 160 pounds 2 ½ drinks remaining 3 drinks remaining
175 pounds N/A 3 ½ drinks remaining
200 pounds N/A 4 drinks remaining

For a woman who weighs 100 pounds, 1 ½ drinks remaining would put her just under the legal limit of .08; for 125 pounds, 2 drinks remaining would put her at just about the legal limit; for 140 pounds to 160 pounds, 2 ½ drinks would leave her close to the legal limit.

For men who weigh 150 pounds, 3 drinks remaining in the body would leave the BAC close to the legal limit; a 175 pound man with 3 ½ drinks remaining would be close to the legal limit and a 200 pound man could have 4 drinks remaining before being close to the legal limit.

For example, let’s say you were to start drinking at 5:00 pm and had two Belgium ales (which are stronger than American beer) and then switched to standard size vodka martinis and drank three of them until time to leave at 9:00 pm. You could figure out where your BAC was in relation to the legal limit by totaling your drinks – the ales count as two each – and getting the result of 4 + 3 = 7. Then count the hours which you have been drinking continuously, four, and subtract that from your total drinks, 7 – 4 = 3. From the table, you can see that all of the women weighing from 100 pounds to 160 pounds would be in danger of being over the legal limit, while men weighing 150 to 160 pounds would be at or close to the limit. So, all you would have to do is remember the number of drinks that applied to your sex and weight and hopefully, be able to count and remember while you are drinking.

The Best Advice? If You Think You Need This Calculation – Don’t Drive!

Remember, this calculation should not be the deciding factor in whether or not you drive. As discussed in previous articles and above, just because a person is not at or close to the legal limit does not mean that they are fit or legal to drive. DUI can be committed and proven based solely upon impairment of normal faculties alone, even if the BAC is less than .08%. It is quite possible and even normal for someone to have a BAC less than the .08% legal limit and still be too intoxicated and impaired from alcohol to drive legally or safely. So be smart and if you are drinking, use a designated driver or a taxi and don’t drive!

In every Florida and Clearwater, St. Petersburg and Tampa Bay area DUI case, there are many factors which need careful analysis by an experienced and aggressive DUI attorney. Sometimes what might seem to be an “open and shut” DUI case may actually be incapable of proof beyond a reasonable doubt by the prosecutor and could result in a dismissal, a not-guilty verdict or a reduction of the DUI charge to a lesser offense or more favorable DUI sentencing by the judge. If you or someone you know is facing a DUI in the Tampa Bay area, call the Office of Clearwater DUI Attorney Garry Potts at (727) 538-4166 today to schedule a free consultation.

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One Response to DUI & Blood Alcohol – How Much is Too Much?

  1. Tatyana Nelson says:

    It’s a great article! You should consider writing books!

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