Blood Alcohol Calculator
Estimated BAC and hours until sober.
Enter your values
Enter the standard drinks you are working with.
Enter the body weight in lb.
Enter the hours since first drink you are working with.
Choose one of: Male, Female.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Estimated BAC and hours until sober. |
|---|---|
| Category | Health |
| Inputs needed | Standard drinks, Body weight, Hours since first drink, Sex |
| Main output | Estimated BAC |
| Formula | BAC = (grams alcohol ÷ (kg × r)) × 100 − 0.015 × hours |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Standard drinks
- Enter the standard drinks you are working with.
- Body weight(lb)
- Enter the body weight in lb.
- Hours since first drink
- Enter the hours since first drink you are working with.
- Sex
- Choose one of: Male, Female.
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.
What do I need to enter into the Blood Alcohol Calculator?
Just 4 values: standard drinks, body weight, hours since first drink, sex. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Blood Alcohol Calculator work out the answer?
The Widmark formula estimates BAC as alcohol grams ÷ (body weight × distribution factor), minus about 0.015% per hour of metabolism. It applies the formula BAC = (grams alcohol ÷ (kg × r)) × 100 − 0.015 × hours and shows the working so you can check each step by hand.
Is the Blood Alcohol Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.