A person’s body size, as determined by height and body weight, can influence his or her blood alcohol concentration (BAC). In general, a shorter person with a smaller body will have a higher BAC than a larger person who consumes the same amount of alcohol over the same period of time. Blood alcohol levels are of extreme importance in DWI/DUI cases, where BAC levels impact a driver’s possible arrest and criminal penalties.
Other factors that may have an effect on someone’s BAC levels include:
rate of consumption.
Note that BAC measures the amount of alcohol in a person’s bloodstream. BAC levels are normally expressed as a percentage. For example, most states consider a BAC of .08% as above the legal limits to drive or operate a motor vehicle.
People that get arrested for a DUI due to their BAC levels should contact a criminal defense attorney or DUI law firm for help. Most lawyers provide free consultations, which means you can get all of your legal questions answered without spending a dime.
1. How does height affect BAC?
People with a smaller body type (as measured by both height and weight) will have higher blood alcohol levels in comparison to people with larger body types. This is true provided the people have the same amount of alcohol consumption over the same period of time.
One reason for this reality is that smaller people have a smaller body mass than people with larger bodies. A smaller mass means the same amount of alcohol gets concentrated in a smaller frame, which translates into higher blood alcohol content levels.
In addition, keep in mind that taller individuals typically have more blood in their bodies than shorter individuals. If the same amount of alcohol gets distributed in a body with relatively low blood content, BAC levels would be much higher when compared to bodies with more blood in their system.
2. Are there other factors that affect a person’s BAC?
Yes. Several factors can affect someone’s BAC levels when drinking. Some of the more common ones include:
weight – an increase in weight usually means that a person can drink more without a drastic rise in BAC levels (to say this another way, people that weigh more will have lower BAC levels when they have the same number of drinks as people who weigh less).
gender – women will generally reach a higher BAC when drinking alcohol at a similar rate to their male counterparts.
rate of consumption – the faster a person drinks alcoholic beverages means the quicker his/her BAC will rise (faster rates of consumption essentially reduce rates regarding the absorption of alcohol in people’s systems).
age – as age increases, the intoxicating effects of alcohol become more pronounced.
stress – this can actually lower the rate of alcohol absorption into a person’s body, which in turn increases a person’s BAC levels. Thus, stress can actually have a lowering effect on a drinker’s blood alcohol levels.
food – people with an empty stomach will absorb alcohol quicker than people with a greater amount of food in their belly. Thus, a party will feel the influence of alcohol faster when they have not eaten in a while.1
3. What does BAC measure?
BAC measures the amount of alcohol in a person’s blood. For example, a BAC of .20% means that someone’s bloodstream contains two parts of alcohol for every 1,000 parts of blood.
BAC is commonly used in DUI charges when police try to establish whether someone is driving under the influence.
Blood alcohol concentration is normally expressed as a percentage – for instance .08%. The higher the number, the more alcohol there is in a person’s bloodstream.
Yes. The federal government says that a BAC of .08% is the “per se” legal limit when it comes to driving intoxicated. A person, then, driving with a BAC of .08% or higher can be arrested and charged for DUI.
Note that individual states have adopted their own BAC rates with regard to DUI charges.
While 49 states follow a .08% per se legal BAC limit, Utah is the only state where the per se BAC limit is not 0.08% – but rather 0.05%.2
States, though, tend to vary with regard to other BAC levels. For example, in California, a BAC of .15% or higher is deemed “excessive,” and drunk drivers with this level will receive steeper DUI penalties (in comparison to drivers with a BAC under .15%).3
In contrast, Idaho law will also impose harsher DUI penalties with excessive BAC levels. But the law defines an excessive BAC as one above .20% rather than .15%.4
Please note that blood alcohol content does not, by itself, determine whether someone’s driving will be impaired by alcohol. Some people may be impaired at a relatively low percentage, while others may be able to drive safely with a relatively high BAC.
But regardless of actual impairment, drivers may not lawfully drive in all states but Utah with a BAC of .08% or higher.
SeePikaar NA, Wedel M, Hermus RJ. Influence of several factors on blood alcohol concentrations after drinking alcohol. Alcohol Alcohol. 1988;23(4):289-97. PMID: 3166629. See also the Stanford University website, “What is BAC?” This web page lists a few other factors that may affect a person’s BAC, including loner periods of time for which drinks are consumed, enzyme production, and medication (including prescription drugs).
A former Los Angeles prosecutor, attorney Neil Shouse graduated with honors from UC Berkeley and Harvard Law School (and completed additional graduate studies at MIT). He has been featured on CNN, Good Morning America, Dr Phil, The Today Show and Court TV. Mr Shouse has been recognized by the National Trial Lawyers as one of the Top 100 Criminal and Top 100 Civil Attorneys.