Blood Alcohol Calculator
Estimated BAC and hours until sober.
Enter your values
ⓘ Live results
Results
- Estimated BAC
- 0.05%
- Legal to drive in the US (0.08)
- Under the limit — but impairment starts far lower
- Hours until zero
- 3.3 hours
- Peak BAC before metabolism
- 0.08%
Quick answer
The Widmark formula estimates BAC as alcohol grams ÷ (body weight × distribution factor), minus about 0.015% per hour of metabolism.
BAC = (grams alcohol ÷ (kg × r)) × 100 − 0.015 × hours
How to use the Blood Alcohol Calculator
- 1Count your standard drinks (14 g alcohol each).
- 2Enter body weight and hours elapsed.
- 3Read the estimated BAC.
Worked example
Using the values the calculator loads with:
Inputs
- Standard drinks3
- Body weight170 lb
- Hours since first drink2
- SexMale
Results
- Estimated BAC0.05%
- Legal to drive in the US (0.08)Under the limit — but impairment starts far lower
- Hours until zero3.3 hours
- Peak BAC before metabolism0.08%
Frequently asked questions
Is this safe to rely on for driving?
No. Individual variation is large, and impairment begins below any legal limit. Never use an estimate to decide whether to drive.
What is a standard drink?
12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits — each contains about 14 g of pure alcohol.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.