In all Australian states, the maximum blood alcohol concentration (BAC) limit for driving is 0.05. This means that you can have a BAC up to this level and still drive. However, understanding how many standard drinks you can have and still drive is a little more complex. 

So, what is BAC? How is it calculated? How many standard drinks can you have and still be under the limit? Does it apply to everyone? This blog will cover everything you need to know about BAC and standard drinks, ensuring you keep yourself, your loved ones, and those you share the road with safe. 

What is BAC?

Blood Alcohol Concentration (BAC) represents the amount of alcohol in your bloodstream, measured as grams of alcohol per 100ml of blood. So a reading of 0.05 means you have 0.05 grams of alcohol per 100ml of blood, or 0.05%. This is what breathalysers measure (and breathalysers are generally accurate to +/- 10% of the value, so if you blow 0.05 it could be as low as 0.045 or as high as 0.055). 

To roughly estimate BAC, people can use online calculators. These provide an approximation based on inputted data. Bear in mind these are inaccurate and your BAC is likely to be significantly higher or lower than the output of these calculators. They should never be relied on when deciding whether to drive after drinking alcohol or not. 

What is A Standard Drink?

A standard drink is equal to 10 grams of pure alcohol. This measure helps to track alcohol consumption more accurately, regardless of the type of alcohol consumed, aiding in making informed choices about alcohol intake and staying within safe consumption limits. 

Let’s look at some examples. 

Calculating Standard Drinks

In Australia, all alcohol bought from a bottle shop must have the number of standard drinks contained within it written somewhere on the label. But the calculation itself is fairly easy. 

Let’s take a schooner of 4% beer. A schooner is 425ml, or 0.425 litres, and the standard gravity of alcohol (the density of alcohol as compared to water) is 0.789. So, the equation is:

0.425 × 4 × 0.789 = 1.34

We then round this to 1.3. So one schooner of 4% beer is equal to 1.3 standard drinks. 

Now let’s also look at a glass of wine. 

A standard glass of wine in a restaurant is usually about 150ml. If we’re drinking a big aussie Shiraz at 14.5% then the equation would be:

0.150 × 14.5 × 0.789 = 1.71

So one glass of a strong red wine is equal to 1.7 standard drinks.

How Many Standard Drinks to Drive?

A commonly used guideline suggests different rules of thumb for men and women. For men, the QLD government recommends no more than two standard drinks in the first hour and no more than one every hour after that. For women, they recommend no more than one standard drink in the first hour and no more than one every hour after that.

However, please note that this is just a rough estimate; alcohol content varies significantly across beverages, and the actual strength of mixed drinks can differ greatly depending on the mix. On top of this, other factors affect your BAC such as body weight, whether you’ve eaten recently, and more.

Does It Apply to Everyone?

The standard of 0.05 BAC applies to drivers of cars, light trucks, and motorcycle riders across various states and territories, ensuring a consistent benchmark for legal driving capabilities. 

However, specific groups, such as learners and provisional drivers, are required to adhere to a 0.00 BAC limit. These strict measures are in place to combat drink driving and enhance road safety. 

Specialised categories of drivers, including those operating heavy vehicles like trucks, public passenger vehicles like taxis and buses, and drivers carrying dangerous goods must also maintain a 0.00 BAC.

Factors That Affect BAC

Determining the exact number of standard drinks you can consume before driving without exceeding the legal BAC limit is impossible, due to the following factors:

Age

As you age, both liver efficiency and the body’s water content decrease, leading to alcohol lingering longer in the body. This results in a slower alcohol metabolism rate.

Sex 

Research shows that enzyme levels in the body play a critical role in alcohol breakdown. Typically, males have higher enzyme levels than females, which enhances their ability to metabolise alcohol more efficiently. As a result, biological sex at birth significantly impacts alcohol tolerance.

Size and Metabolism

Individuals with a larger body size tend to be able to tolerate larger amounts of alcohol. Additionally, metabolism speed influences alcohol processing. Also, muscle – having more water content than fat – dilutes alcohol in the blood, meaning that those with higher muscle mass can generally tolerate more alcohol.

Food Intake and Empty Stomach 

Consuming alcohol on an empty stomach can lead to quicker absorption into the bloodstream, potentially raising your BAC to higher levels compared to drinking after eating. Food in the stomach slows the absorption of alcohol, moderating its effects.

Medication 

Medications can interfere with how the body absorbs and metabolises alcohol, as both may require liver processing. This competition can slow alcohol breakdown, potentially increasing BAC levels. It’s crucial to consult healthcare professionals when mixing alcohol and medications to prevent serious reactions.

Can You Lower BAC Quickly?

Reducing BAC levels more rapidly isn’t feasible through any quick-fix methods. The liver metabolises alcohol at a consistent rate, approximately one standard drink per hour. Attempts to lower BAC faster, such as drinking coffee or taking cold showers, are ineffective. The only sure way to reduce BAC is time; allowing the body to process and eliminate the alcohol naturally. It’s crucial to plan accordingly, considering this fixed rate, to ensure safety and legality when drinking and potentially driving later.

Seek Legal Advice At Donnelly Law Group

Every day, we assist individuals in consulting their drink driving issues to achieve the most favourable outcomes, aiming to restore their licences and livelihood promptly. Our support extends to a diverse group, including workers concerned about their careers, parents and carers dependent on driving, commercial drivers, and those with or without prior convictions. We understand the broader implications of a criminal record on employment, travel, and insurance. 

If you’re seeking legal advice or representation in Queensland, Donnelly Law Group is here to help. Contact us today, and let our experienced criminal lawyers in Queensland guide you through your legal challenges with confidence and skill.