BAC: What It Means and Why It Matters

April 19, 2017
Sobriety Test

Blood alcohol content (BAC) is the measure of alcohol present in your blood at a given moment. Technically speaking, the measure tells how many milligrams of alcohol are contained in 100 milligrams of your blood. For most people, it’s easiest to understand as a raw percentage: a BAC of 0.08% would mean every 10,000 mg of your blood contains 8 mg of alcohol.

That number—0.08%—is an important one: there is no state in which a person can legally drive with a BAC over 0.08% (although some have enhanced penalties for even higher BACs). In fact, nearly a third of all traffic fatalities in the US involve at least one driver with a BAC over 0.08%.

Online, it’s easy to find calculators and charts that estimate BAC—in fact, we’ve attached one at the bottom of this post. However, tools like those can only provide a rough estimate of BAC; the only way to know your BAC at any given moment is with a personal breathalyzer. This is because each body metabolizes alcohol differently, based on multiple factors:

BAC Factors

How old are you? The older you are, the less efficiently your body process alcohol and therefore the higher your BAC will be with each drink.

What gender are you? In general, women experience higher BAC than men for the same number of drinks, since their lower stomach enzymes break down alcohol more slowly. Additionally, women’s bodies contain less water than men’s, which means there’s less water to dilute the alcohol they consume.

What’s your body size? Heavier people contain more water and thus greater dilution of the alcohol they consume. Conversely, lean people contain less water, which explains why they experience alcohol’s effects much more quickly than their larger companions.

What’s your body type? Fats aren’t water-soluble, which means there’s little water in them to absorb alcohol from the bloodstream. This means the alcohol has nowhere to go until the liver can deal with it. On the other hand, muscle tissues are able to absorb alcohol; thus, more muscular people can typically absorb more alcohol than their less fit counterparts without elevated BAC.

What’s your metabolic rate? Each body processes alcohol at its own rate, which varies widely across the human species. Faster metabolisms can process more alcohol in a short timespan, minimized the alcohol’s effect on BAC.

How do you feel? People under stress can consume more alcohol as their body shunts blood from your digestive system to your muscles; this biological response minimizes alcohol flow into your bloodstream. However, as stress dissipates, BAC may increase rapidly as your body’s blood flow returns to normal.

What are you on? Mixing alcohol with drugs—prescription or otherwise—is a formula for disaster. Many drugs ramp up alcohol’s adverse effects, and some can present severe health risks if mixed with alcohol.

What have you eaten? An empty stomach permits alcohol to flood the bloodstream; on the other hand, a full stomach—particularly if it’s a starchy food like bread—can keep alcohol on “hold” for longer, letting it enter the bloodstream at a more measured pace.

Beyond these metabolic/biological concerns, there are other factors affecting a body’s BAC at any given point:

What did you drink? Obviously, the more alcohol each drink contains, the more alcohol you are putting into your system. There’s a massive difference between five beers, five glasses of wine, and five shots.

How fast did you drink? Again, it’s all about rate of absorption: slowly sipping five glasses of wine over a three hour party is a far cry from slamming five shots on your way in the door.

With that many moving parts in play, it’s obviously a terrible idea to try and beat a breathalyzer if you have been drinking. A system like Soberlink is even harder to beat because a .000 BAC is expected and anything above that will trigger retests to confirm that you have consumed alcohol.

BAC Chart for Men & Women

BAC chart

About the Author

Soberlink supports accountability for sobriety through a comprehensive alcohol monitoring system. Combining a breathalyzer with wireless connectivity, the portable design and technology includes facial recognition, tamper detection and real-time reporting. Soberlink proves sobriety with reliability to foster trust and peace of mind.

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