Does a high alcohol tolerance mean a lower BAC?

No. Tolerance changes how drunk you feel, not how much alcohol is in your blood. Two people who drink the same amount can have a similar BAC even if one feels far more affected than the other — and both are equally impaired behind the wheel.

Blood alcohol levels: what each BAC actually means

Q: What is a safe blood alcohol level?

There is no blood alcohol level that is truly safe for driving. Legally, fully licensed drivers in Australia must stay under 0.05, and learner and probationary drivers must be at zero. But judgement, reaction time and coordination are all affected below 0.05, so the only completely safe level for driving is 0.00.

Q: At what BAC do you start to feel drunk?

Most people notice a feeling of wellbeing, talkativeness and relaxation up to about 0.05. Between 0.05 and 0.08, judgement is impaired and inhibitions drop. Slurred speech and loss of balance and coordination typically appear from around 0.08 upward — but subtle impairment of driving skills begins much earlier.

Q: What BAC level is dangerous?

A BAC of 0.15 to 0.30 is a high-risk state that can cause inadequate breathing, an inability to walk unaided, loss of bladder control and unconsciousness. Above 0.30, alcohol can cause a coma or death. A very high or rising BAC with vomiting, seizures or slow or irregular breathing is a medical emergency — call 000.

Q: How can I tell what my blood alcohol level is?

The only accurate measure is a breath or blood test. A drink-tracking app or a Widmark-formula calculator can estimate your BAC from what you have consumed, your weight and the time elapsed, but it is only an estimate and should never be used to decide whether you are fit to drive.

Your blood alcohol level is a single number, but it maps onto a whole range of effects — from a relaxed buzz to a life-threatening emergency. Here's what each level does to your body and your driving, and why the number matters more than how you feel.

What is blood alcohol concentration?

Blood alcohol concentration — BAC — measures how much alcohol is in your bloodstream. In Australia it's written as a percentage: a BAC of 0.05% means there are 0.05 grams of alcohol in every 100 millilitres of blood, as the Alcohol and Drug Foundation explains. People usually drop the percent sign and just say "point oh five".

The reason BAC is so useful is that it's a far better guide to how affected you are than counting glasses. Two people can drink the same amount and reach very different levels, and the same person can hit different levels on different nights depending on food, timing and a dozen other factors. The number is what your body — and a breathalyser — actually responds to.

BAC levels and their effects

The effects of alcohol climb steadily as your BAC rises. The bands below follow the guide published by SA Health. They're a general picture — the exact level at which any one person feels each effect varies — but the direction of travel is the same for everyone.

BAC	Typical effects
Up to 0.05	A feeling of wellbeing — more talkative, more relaxed and more confident. Reaction time and judgement are already slightly affected.
0.05 – 0.08	Impaired judgement and reduced inhibitions. You take risks you normally wouldn't and misjudge your own ability.
0.08 – 0.15	A genuinely risky state: slurred speech, impaired balance and coordination, unstable emotions, and often nausea or vomiting.
0.15 – 0.30	High risk: inadequate breathing, being unable to walk without help, loss of bladder control, and possible unconsciousness.
Over 0.30	Can cause a coma, or result in death.

The pattern worth noticing is that the pleasant part of the curve is short and near the bottom. The confidence and relaxation of a low BAC give way to poor judgement, then to loss of physical control, then to real danger — and because a rising BAC dulls your ability to judge yourself, the point where you'd want to stop is exactly the point where you're least equipped to notice it.

Impairment starts well below 0.05

It's tempting to treat 0.05 as a line where impairment switches on. It isn't. As the Alcohol and Drug Foundation puts it, "even very small amounts of alcohol can affect your concentration, judgement and performance", and "even if you're below 0.05% BAC, your judgement, reaction times and driving skills are impacted".

That's why the legal limit and the safe limit aren't the same thing. Being under 0.05 keeps you within the law if you hold a full licence, but it doesn't mean alcohol isn't affecting you. The only blood alcohol level with no impairment at all is zero.

What each level means behind the wheel

Driving is where BAC matters most, because the crash risk rises far faster than the number itself. Victoria's Transport Accident Commission reports that at 0.08 a driver is around five times more likely to be involved in a crash, and between 0.08 and 0.12 up to ten times more likely.

The specific skills alcohol erodes shift as BAC climbs:

0.02 – 0.05: vision and the ability to judge distance decline, willingness to take risks goes up, and you respond more slowly to more than one thing happening at once.
0.05 – 0.08: distance judgement worsens further, sensitivity to red lights drops, reactions slow and concentration gets shorter.
0.08 – 0.12: overconfidence sets in, driving becomes reckless, and peripheral vision and the ability to spot hazards suffer.

This is the core reason Australia's limit is 0.05 for full-licence drivers and zero for learner and probationary drivers. Even the earliest band — from just 0.02 — already chips away at the exact skills driving depends on.

Why your BAC isn't the same as your mate's

Two people can share a bottle of wine and end the night at completely different levels. The main things that change how high your BAC climbs from the same drinks include:

Body size and body-fat percentage — alcohol spreads through body water, so a smaller person, or one with more body fat and less water, reaches a higher concentration.
Sex — on average women reach a higher BAC than men from the same drinks, for reasons covered in our guide on why alcohol affects women differently.
Food — drinking on an empty stomach sends alcohol into your blood faster and pushes your peak BAC higher.
Age, liver health and medications — all change how quickly you absorb and clear alcohol.
Drink strength — a "drink" can be anything from half a standard drink to three, so the pour matters as much as the count. Our standard drinks calculator shows what common drinks really add up to.

One thing that doesn't lower your BAC is tolerance. A regular drinker may feel less affected at a given level, but the alcohol in their blood — and their impairment behind the wheel — is the same. Feeling fine is not the same as being under the limit.

How long each level takes to clear

Once you stop drinking, your BAC falls at a fixed pace — roughly one standard drink, or about 0.015%, per hour. Nothing speeds it up: not coffee, not a cold shower, not food, not sleep. A BAC of 0.15 can take around ten hours to reach zero, which is why a big night can leave you over the limit well into the next morning. We cover the maths in how long until my BAC is zero and the morning-after risk in can I drive the morning after drinking.

When a high BAC becomes an emergency. A BAC in the 0.15–0.30 range and above can suppress breathing and consciousness, and above 0.30 it can be fatal. If someone is confused, vomiting, having a seizure, breathing slowly or irregularly, has cold or bluish skin, or can't be woken, treat it as suspected alcohol poisoning and call 000 straight away — remember that BAC keeps rising for a while after the last drink. See the signs of alcohol poisoning for what to watch for and what to do while you wait.

A note on driving: in Australia the legal limit is under 0.05 for full-licence drivers and zero for learners and P-platers. No app, calculator or personal breathalyser can tell you that you're safe to drive — impairment starts below 0.05, and every BAC estimate carries real uncertainty. If you've been drinking, the safe choice is not to drive. As a broader guide, the NHMRC recommends healthy adults have no more than 10 standard drinks a week and no more than 4 in a day to keep health risks low.

Frequently asked questions

What is a safe blood alcohol level?

For driving, there isn't one above zero. Full-licence drivers must stay under 0.05 and learner and probationary drivers at zero, but judgement and reaction time are affected below 0.05, so only 0.00 carries no impairment.

At what BAC do you start to feel drunk?

Wellbeing and talkativeness appear up to about 0.05; judgement and inhibitions go between 0.05 and 0.08; slurring and loss of coordination usually start around 0.08. Driving skills, though, are affected from as low as 0.02.

What BAC level is dangerous?

From 0.15 to 0.30 is a high-risk state that can cause poor breathing, an inability to walk unaided and unconsciousness. Above 0.30 alcohol can cause a coma or death. Treat a very high BAC with those signs as an emergency and call 000.

Does a high tolerance mean a lower BAC?

No. Tolerance changes how drunk you feel, not the amount of alcohol in your blood or how impaired you are. You can feel fine and still be over the limit.

How can I tell what my blood alcohol level is?

Only a breath or blood test measures it accurately. A drink-tracking app can estimate it from what you've had, your weight and the time elapsed — useful for awareness, but never a fitness-to-drive test.