Blood Alcohol Content (BAC) Calculator — Widmark Formula
Estimate blood alcohol concentration from standard drinks, body weight and hours elapsed.
Last reviewed by the myCalculator Editorial Team
Input Parameters
One Australian standard drink contains 10 g of pure alcohol.
Calculation Results
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Formula & How Blood Alcohol Content (BAC) Calculator — Widmark Formula Works
The Widmark formula estimates blood alcohol from the mass of alcohol consumed divided by body water volume, then subtracts elimination at roughly 0.015% per hour. Individual results vary widely with food intake, liver function, medication, hydration and drinking rate, so this is an educational estimate only and can be materially wrong for any given person. Worked example: four standard drinks contain about 40 g of alcohol. For a 75 kg man (distribution factor 0.68) the Widmark estimate is 40 ÷ (75 × 0.68 × 10) = 0.078%, and after 2 hours of elimination at about 0.015% per hour it is roughly 0.048%. Real BAC varies a lot between people and with food and drink strength, so never use this estimate to decide whether you are safe to drive. The only safe approach is not to drive after drinking.
- Enter Body Weight (kg) (kg): Input your target parameter value.
- Enter Body Water Distribution Factor: Input your target parameter value.
- Enter Australian Standard Drinks Consumed (drinks): Input your target parameter value.
- Enter Hours Since First Drink (hours): Input your target parameter value.
- Apply Formula: Calculate using
BAC = (A × 5.14 / (W × r)) - (0.015 × H), where A = alcohol oz, W = weight lb. - Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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Frequently Asked Questions (FAQs)
Can a BAC calculator tell me if I am safe to drive?
No. The Widmark formula is a population estimate with wide individual variance and cannot account for food, medication or metabolism. Never use it to decide whether to drive — if you have been drinking, do not drive.
How long does it take to sober up?
The body eliminates alcohol at roughly 0.015% BAC per hour and nothing speeds it up. Coffee, cold showers, food and exercise affect alertness but not blood alcohol concentration.
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Authoritative Standards & Verified Reference Citations
Calculations and mathematical logic on this page are grounded in published statutory rules, regulatory standards, and official government data published by the following bodies:
Australia's Physical Activity and Sedentary Behaviour Guidelines and dietary energy expenditure metrics.
Nutrient Reference Values (NRVs) for Australia and New Zealand, macronutrient distribution, and hydration standards.
Dedicated Australian home loans, borrowing capacity, mortgage repayments & refinance modeling.