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.