Oftentimes in my practice, I encounter a client who has been charged with a DUI and cannot believe their alcohol content was over the legal limit since they only had a few drinks before driving. Many people encounter this same issue when they go out to a bar; a friend or colleague inevitably leaves indicating they only had a couple of beers and they are “fine” to drive. So that beckons the question: How many drinks can you have before you are over the legal limit?
In order to answer that question, we must first define exactly what the “legal limit” is. This is important because it differs depending on the context. For example, in Ontario, a novice driver or young driver (under 21 years of age) cannot operate a motor vehicle with any alcohol in their system1. In addition, any motorist may be subject to a discretionary license suspension if they have over 50 milligrams of alcohol per 100 mL of blood2.
Both above situations are offences under the Highway Traffic Act. Therefore, they are not criminal offences. When individuals are arrested and charged with a DUI, they commonly are referring to the criminal offence of drinking and driving. In Canada, there are two such offences: Impaired Operation3 and Over 804. The second of those offences (Over 80) will form the subject of the remainder of this article. It makes it a criminal offence to operate a motor vehicle while having greater than 80 milligrams (mg) of alcohol per 100 millilitres (mL) of blood.
Before discussing the data on how many drinks it would take for you to get over 80 mg of alcohol per 100 mL of blood, it is important to understand that the criminal offence of Impaired Operation makes it an offence to operate a motor vehicle while your ability to drive is impaired “to any degree” by alcohol5. This means even if your blood alcohol content is lower than 80 mg of alcohol per 100 mL of blood, it is still possible to be charged with the criminal offence of Impaired driving if the officer observes any indicators of impairment such as poor driving, bloodshot eyes, slurred speech etc.… If this is the situation you find yourself in, you should get in contact with an experienced DUI lawyer to discuss your options.
Now we get to the good stuff; how many drinks can you have before you would reach that 80mg per 100 mL of blood threshold? Unfortunately, there is no hard and fast rule to this question. The answer, as is the case to most legal questions, is that it varies. It will depend on a variety of factors which include (but are not limited to) your weight, sex, timeframe of drinking and individual genetics.
If you are looking for an estimate, the most commonly used formula to calculate your blood alcohol content is the Widmark formula6 7. Before discussing the details of this formula, please note that this is for informational purposes only!! Please DO NOT treat the information in this article as a substitute for legal advice nor as a basis to believe it can be relied upon to avoid being charged with a DUI if you choose to have some drinks before driving. Individual genetics vary, and the calculation below is simply an estimate. In addition, the Criminal Code presumes a properly functioning breathalyzer machine operated correctly by a qualified technician is definitive proof of your blood alcohol content8. Therefore, in most cases the calculation will not assist you in proving your blood alcohol content was lower than the results shown from the breathalyzer machine.
The Widmark formula uses the following calculation to provide an estimate of your blood alcohol content:
C = (A x 100) / ( r x W ) − (β x t)
where C is the blood alcohol concentration (expressed as a decimal i.e. 80 mg of alcohol per 100 mL of blood would be expressed as 0.08); A is the mass of alcohol consumed (in grams); r is the Widmark factor; W is body weight (in grams); t is elapsed time since the start of drinking (in hours); and β is the elimination rate. The Widmark factor r is variable and depends on body mass, percentage body fat, age, and sex. In his research, Widmark found that the average Widmark factor for men was 0.68 and for women was 0.55. The average elimination rate is 0.018g% per hour9.
As you can see, the formula can get quite complicated. But for the purposes of this article, we can take the averages for simplification, convert the units and rearrange the formula to determine how many drinks it would take to meet the 80 mg per 100 mL threshold. If we assume a standard drink has approximately 14g of alcohol per drink (which is the case in Canada and the US10), the calculation will be as follows:
For men:
# of Drinks = (0.08 + (0.018 x time since start of drinking)) x (0.22 x weight in lbs)
For Women:
# of Drinks = (0.08 + (0.018 x time since start of drinking)) x (0.178 x weight in lbs)
Example:
Question:
John Smith is a 200 lb male who was recently charged with a DUI (Over 80) for being over the legal limit while driving after a night out with friends. On the night of his arrest, John had 8 standard drinks from 10pm to 2am. He was stopped in his motor vehicle and arrested by police at 2am. John wants to know in retrospect, how many drinks he could have had that evening before reaching the legal limit. According to the Widmark formula, if John is an average male, approximately how many drinks could John have had before reaching the legal limit?
Answer:
John is a male, so if we use the above formula, and plug in the numbers from our fact scenario, the formula looks like the following:
# of Drinks = (0.08 + (0.018 x time since start of drinking)) x (0.22 x weight in lbs)
= (0.08 + (0.018 x 4 hours)) x (0.22 x 200 lbs)
= 6.688
Therefore, the Widmark formula would indicate John could have had approximately 6.688 drinks before reaching the legal limit of 0.08 or 80 mg of alcohol per 100 mL of blood in that timeframe.
I hope the above information is helpful from an informational perspective, but again, please do not use it as a substitute for legal advice. The only truly safe way to avoid being charged with a DUI is when choosing to drink, don’t drive. If you do find yourself in the unfortunate situation where you have been charged with a DUI, please contact Nadi Law to speak with an experienced criminal lawyer!
