How Australian standard drinks are defined, how BAC is estimated using the Widmark formula, the 0.05 legal limit, and why no calculator can guarantee you're safe to drive.
In Australia, one standard drink always equals 10 grams of pure alcohol, regardless of the beverage type. This is a fixed national definition — different to some other countries, such as the UK which uses 8 grams per unit.
| Drink | Typical Serve | Standard Drinks |
|---|---|---|
| Mid-strength beer (3.5%) | 375ml can/bottle | ~1.0 |
| Full-strength beer (4.8%) | 375ml can/bottle | ~1.4 |
| Wine (13%) | 150ml glass | ~1.5 |
| Spirits (40%) | 30ml shot | ~1.0 |
Note that a standard restaurant or bar pour is often larger than these reference serves — a generous wine pour or a double spirit measure can easily be 1.5-2 standard drinks rather than 1.
| Licence Type | Legal BAC Limit |
|---|---|
| Full licence | Below 0.05% |
| Learner (L-plate) | 0.00% |
| Provisional (P-plate) | 0.00% |
| Heavy vehicle / bus / dangerous goods | 0.02% (some states require 0.00%) |
A BAC of 0.05% means there is 0.05 grams of alcohol present for every 100ml of blood. Random Breath Testing is actively enforced across every Australian state and territory.
Get an estimated blood alcohol reading based on your drinks, weight and time elapsed.
Open BAC Calculator →Most BAC calculators use a version of the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s. It estimates BAC based on total alcohol consumed, body weight, a sex-based distribution constant, and time elapsed since drinking began.
The formula accounts for the fact that alcohol distributes through total body water, and men and women have different average body water proportions — which is why the same number of drinks typically produces a different estimated BAC for a man versus a woman of similar weight.
The body metabolises alcohol at a roughly fixed rate of approximately 0.015% BAC per hour — broadly equivalent to one standard drink per hour for an average adult. This is a biological constant, not something that can be sped up.
This is the single most important thing to understand about any BAC calculator, including ours: it provides an estimate, not a guaranteed measurement. Real BAC is affected by many individual factors a calculator cannot fully account for — food intake, medication, individual metabolism, hydration, and even genetic variation in alcohol-processing enzymes.
The Widmark formula and every calculator built on it rest on population averages. Your actual blood alcohol concentration at any moment depends on factors the formula cannot know.
Because of this, two people who drank identically can return meaningfully different readings on a police breathalyser. The formula produces a single number; reality produces a range.
Your liver metabolises alcohol at a broadly fixed rate. Nothing reliably speeds it up.
This is why drinking late into the night frequently leaves people over the limit the following morning. If you finished drinking heavily at 2am, you may still be above the legal limit at 9am. Morning-after drink driving offences are common in Australia for exactly this reason, and people are routinely surprised by them.
The general limit for a fully licensed driver in Australia is 0.05, but a zero BAC requirement applies to a number of categories, which commonly include learner and provisional drivers, and drivers of certain vehicles such as heavy vehicles, taxis, rideshare vehicles, and public passenger vehicles.
The specific categories, limits, and penalties are set by each state and territory and differ between them. If you hold a learner or provisional licence, or drive professionally, the applicable limit for you is almost certainly zero — check the rules of your state or territory road authority rather than assuming the general limit applies.
It is worth stating this plainly, because it is the single most important thing on this page.
If you have been drinking, do not drive. The only reliable approach is not to drive at all. Plan a taxi, a rideshare, public transport, or a designated driver before you start drinking, not after.
A BAC calculator is an educational tool for understanding how alcohol behaves in the body — how standard drinks are defined, why clearance takes time, and why nothing accelerates it. It is not, and cannot be, a tool for deciding whether to drive.
Individual variation is large, poured drinks are unreliable measures, impairment starts below the legal limit, and only a calibrated breathalyser measures what is actually in your blood. If you have consumed alcohol, arrange another way home.
This page provides general information only and is not legal or medical advice. Legal limits, licence categories, and penalties are set by each state and territory. If you are concerned about your drinking, speak with your GP, or contact the National Alcohol and Other Drug Hotline on 1800 250 015 for free, confidential advice.