Blood Alcohol Concentration Calculator
Estimate blood alcohol concentration using the Widmark formula from standard drinks (10g alcohol), body weight, sex and time elapsed.
Your results
Educational estimate only using the Widmark formula. Never use this to decide whether it is safe to drive — actual BAC varies widely between individuals.
Calculation breakdown
- Widmark formula
- BAC% = (grams of alcohol ÷ (weight(g) × distribution ratio)) × 100 − (0.015 × hours elapsed)
Worked example
An 80 kg man who has had 4 standard drinks (40 g of alcohol) over 2 hours has an estimated BAC of around 0.043%, using a distribution ratio of 0.68.
Assumptions
- Uses the Australian standard drink definition of 10 grams of alcohol.
- Assumes an average elimination rate of 0.015% BAC per hour; individual metabolism varies considerably.
- This is an educational estimate only and must not be used to judge fitness to drive.
How this calculator works
This calculator estimates blood alcohol concentration (BAC) using the Widmark formula, based on the number of Australian standard drinks (each containing 10 grams of alcohol), body weight, sex and hours since drinking began. It is intended as a rough educational estimate only and must never be used to decide whether it is safe to drive.
Frequently asked questions
What is a standard drink in Australia?
An Australian standard drink contains 10 grams of pure alcohol, which this calculator uses as the base unit for the BAC estimate.
Is this calculator accurate enough to decide if I can drive?
No. BAC estimates vary significantly between individuals due to metabolism, food intake and other factors; never rely on this to decide whether to drive.
How does body weight affect BAC?
A higher body weight generally distributes alcohol through more body water, resulting in a lower estimated BAC for the same number of drinks.
Results are estimates only and are not financial, tax, legal or credit advice.