The police are your friends — as long as you’re not doing anything wrong. Even so, many of us still get a sinking feeling when we see those blue lights behind us on the road.

You might have been out with your friends celebrating a birthday or promotion and had a few drinks at the party. You figured you were okay to drive, but now you’re not so sure.

Before you go out on Australia’s roads with alcohol in your bloodstream, you need to understand the legal limits and what it takes to reach them.

Understanding Blood Alcohol Limits

When you drink alcohol, your body absorbs it into the bloodstream. Alcohol stays present in your body for a period of time after you drink it.

This is what law enforcement officers use to determine if you are safe to drive. They will measure your BAC using a machine called a breathalyzer. You blow into the machine and it roughly calculates your BAC.

If the breathalyzer registers over the limit, you’ll be taken to the police station for a second, evidentiary test. If this test is also over, you’ll be charged with a DUI.

According to Riviere Law, the maximum limit for all drivers on Australian roads is 0.05%. This means that for every 100 ml of blood, there is 0.05 g of alcohol in your bloodstream.

However, some drivers are subject to an even stricter limit. People driving taxis, buses, vehicles with dangerous goods or large vehicles over 13.9 tonnes must keep their BAC under 0.02%. F

Furthermore, learner drivers, Provisional 1 or 2 drivers, and anyone from overseas holding an equivalent licence must maintain a BAC of absolutely zero.

You are required to know the limit that applies to you. Citing ignorance or misunderstanding the law is not a valid defence in Australian courts.

How Many Drinks to Hit Your Limit?

The next question is, how many drinks can you have before you hit your limit? Is there a good way to keep track? Let’s find out.

There’s a rule of thumb that you may have heard. You can have two drinks in the first hour and one drink every hour after that and still stay under 0.05% BAC. However, the idea of counting drinks and keeping track of your BAC is shaky at best — for more than one reason.

BAC Factors

The same amount of alcohol will affect two individuals very differently. It can even affect the same individual differently on different days.

More body mass, eating food with your drink, having a healthy liver, and being physically well all slow the absorption of alcohol into your bloodstream. In other words, it will require more alcohol to raise your BAC to 0.05% if you have one or more of these factors.

High fat to lean muscle ratio, unhealthy liver function, feeling stressed or tired, and being unused to alcohol are all factors that generally raise your BAC faster.

In short, it’s hard to know exactly how much alcohol you can consume before you reach 0.05%. For one person it might be 4 beers. For another, it might only be two.

Amount of Alcohol

It’s also very hard to define and keep track of the amount of alcohol you’re actually consuming. The “rule of thumb” we mentioned earlier is based on a standard drink size. However, the size of alcoholic drinks is all over the map — not to mention that the alcohol content of a given drink can vary drastically.

For example, a light beer might contain only 2.5% alcohol, but a shot of vodka will generally contain a whopping 40%! You could drink considerably more of those beers before they would affect you as much as one shot of vodka.

Wine glasses range from 100ml in size to over 280ml and pre-mixed drinks come in a variety of sizes. There should be a label indicating how many standard drinks are in a bottle, but how many people actually look at that and consider it?

Then, there is the concern of how much alcohol is in a given drink. Bartenders don’t always measure mixed drinks exactly when making them and some may be more generous than others with the spirits. Plus, how do you count the top-ups?

It gets confusing and hard to keep track of quickly!

Staying Under Your Limit

In all reality, the only way to truly know your BAC is under the legal limit is to not drink before driving. There just isn’t a good way to measure.

More than a quarter of Australian drivers and riders who die in car accidents have a BAC that is over the legal limit. Stay safe on the roads and protect your fellow citizens. Have someone else drive when you’ve been drinking for everyone’s safety.