Blood Alcohol Concentration Calculator
Estimate your BAC using the Widmark formula, calibrated for Australian standard drinks (10g pure alcohol) and legal limits. This is not to be used when you have been drinking and is not advice. It is a rough way to estimate something that differs greatly depending on lots of facts such as weight, height, liver function etc.
Our advice is that if you have been drinking you should never drive. You should always get someone else to drive or take public transport. The purpose of this calculator is that people are often surprised by how high their readings are after they have been arrested for drink driving. Hopefully this calculator will show you how fast the readings can get very high and emphasize the need to avoid drinking and driving.
Your Details
What You Drank
Your Estimated BAC
Your BAC vs Australian Legal Limits
BAC Effects Guide
| BAC (%) | Effects & Behaviour | Impairment | AU Legal Status |
|---|---|---|---|
| 0.000–0.019 | Appears normal. Slight relaxation possible. | Subtle — detectable only with special tests | ✓ Legal (all licences) |
| 0.020–0.049 | Mild euphoria, relaxation, talkativeness, reduced inhibition | Concentration, judgement begins to decline | ⚠ Over 0.02 limit (HV/Commercial) |
| 0.050–0.079 | Reduced sensitivity to pain, euphoria, disinhibition, extraversion | Reasoning, depth perception, peripheral vision, glare recovery | ✗ Over legal limit (Full licence) |
| 0.080–0.149 | Over-expression, boisterousness, possible nausea | Reflexes, reaction time, gross motor control, slurred speech | ✗ Drink driving (increased penalties) |
| 0.150–0.299 | Nausea, vomiting, emotional swings, partial disorientation | Severe motor impairment, memory blackout possible | ✗ High-range — mandatory interlock / imprisonment |
| 0.300–0.399 | Stupor, CNS depression, lapses of consciousness | Bladder, breathing, heart rate, balance severely impaired | ☠ Danger of death — call 000 |
| >0.400 | Coma, severe CNS depression | High risk of fatal respiratory arrest | ☠ Medical emergency — call 000 |
Australian Law & BAC
One Australian standard drink contains 10 grams of pure alcohol. Examples: a 285ml pot/middy of full-strength beer (4.8% ABV) ≈ 1.1 standard drinks; a 425ml schooner of full-strength beer ≈ 1.6 standard drinks; a 30ml nip of spirits (40% ABV) ≈ 1.0 standard drink; a 150ml glass of wine (13% ABV) ≈ 1.5 standard drinks.
0.05% — Full licence holders (all states & territories). 0.02% — Heavy vehicle drivers (>13.9t GVM in NSW; >15t in other states), public passenger vehicles (taxis, buses), vehicles carrying dangerous goods. 0.00% — Learner drivers (L plates), Provisional / P-plate drivers (P1 & P2), overseas/interstate learner/provisional equivalent holders, and most commercial operators. If in doubt about your specific category, check your state’s transport authority.
BAC = (Alcohol in grams ÷ (Body weight in grams × r)) − (0.015 × hours elapsed)
Where r = 0.68 for males, 0.55 for females (Widmark ratio, reflecting body water distribution). The liver metabolises alcohol at approximately 0.015% BAC per hour, though this varies significantly between individuals.
This calculator provides an estimate only. Actual BAC depends on many individual factors including food consumption, medication, metabolism, liver health, and hydration. It cannot replace a breathalyser or blood test. Never drive after drinking. Random breath testing (RBT) operates across all Australian states and territories 24/7.