Blood Alcohol Calculator Australia

Why Australia Counts in Standard Drinks

Most international BAC tools assume a US "standard drink" of about 14 grams of alcohol. Australia is different: here a standard drink contains exactly 10 grams of pure alcohol. That single difference changes the maths, so a calculator tuned for the US will understate how many standard drinks you have actually had. This tool uses the Australian 10g definition, which lines up with the figures printed on every can, bottle and cask sold in Australia.

A standard drink is smaller than most people expect. A 375ml can of full-strength beer is about 1.4 standard drinks, a restaurant glass of wine can be 1.5 to 1.8, and a generous home pour of spirits can quietly be two. Counting actual standard drinks — not glasses — is the foundation of an honest BAC estimate. Mid-strength and light beers contain less alcohol per can, while pre-mixed spirits and cocktails are notoriously easy to underestimate, so the label is your best friend.

The same logic explains why two people drinking "the same amount" can end up with very different BACs. A lighter person, or anyone drinking spirits rather than light beer, accumulates grams of alcohol faster than the social label "a few drinks" suggests.

The Widmark Formula, Australian Edition

The calculator uses the Widmark formula, the forensic standard for estimating BAC:

BAC% = [ (standard drinks × 10) / (weight in grams × r) ] × 100 − (0.015 × hours)

Here r is the volume-of-distribution constant: 0.68 for men and 0.55 for women, reflecting differences in body-water percentage. The final term subtracts the alcohol your liver has already eliminated at roughly 0.015% per hour.

Worked Example: Friday Night at the Pub

Imagine Liam, an 85kg man on a full licence. Over three hours he drinks four 375ml cans of full-strength beer — about 5.6 standard drinks, or 56 grams of alcohol.

1. Volume of distribution: 85,000g × 0.68 = 57,800.
2. Raw BAC: (56 / 57,800) × 100 = 0.0969%.
3. Subtract elimination: 0.015 × 3 hours = 0.045.
4. Estimated BAC: 0.0969 − 0.045 = 0.052%.

Liam is just over the 0.05 full-licence limit. To drop below 0.05 he needs about (0.052 − 0.05) / 0.015 ≈ 0.1 hours, and to reach 0.00 he needs roughly 3.5 more hours. Now picture his mate Ava on her P-plates: with a 0.00 limit, even one standard drink would put her over. The licence type completely changes the verdict from the same drinks.

Reading Your Result

The tool shows three numbers that matter:

• Your limit — 0.05 for a full licence, 0.00 for learner and provisional drivers.
• Time under limit — how long until your estimate falls below your legal threshold.
• Time to zero — when all alcohol should, on average, be gone.

If you want to plan a big night responsibly, pair this with our BAC Calculator for the US 14g model, or check recovery the next day with the Water Intake Calculator.

A Serious Safety Note

This is an estimate, not a breathalyser reading. Drink strength, food, hydration, medication, fatigue and individual metabolism all shift real BAC, and police testing measures what is actually in your blood. The figures here are for education and planning only. If you have had any alcohol, the safest BAC for driving is always 0.00 — never drink and drive. When in doubt, leave the car, call a taxi or rideshare, or wait it out.