Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
Estimated BAC
0.048
Status
Over the 0.04% commercial limit
Hours until roughly zero
3.2
Hours until below 0.08%
0.0
Peak BAC before metabolism
0.078
Standard drinks counted
3.0
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter standard drinks.
- 2Enter body weight (lb).
- 3Enter sex.
- 4Enter hours since first drink.
- 5Read your estimated bac on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
The Widmark formula estimates blood alcohol from body water distribution. It is an estimate only — food, medication, and individual metabolism shift the real number. Never use it to decide whether to drive.
Worked example
Using the values the calculator loads with:
Inputs
- Standard drinks: 3
- Body weight: 175 lb
- Sex: Male
- Hours since first drink: 2
Results
- Estimated BAC: 0.048
- Status: Over the 0.04% commercial limit
- Hours until roughly zero: 3.2
- Hours until below 0.08%: 0
- Peak BAC before metabolism: 0.078
- Standard drinks counted: 3
What each field means
Inputs
- Standard drinks
- The standard drinks used in the calculation. Starts at 3 so you have a working example on load. Accepted range: 0–25.
- Body weight (lb)
- The body weight used in the calculation, measured in lb. Starts at 175 lb so you have a working example on load. Accepted range: 80–400 lb.
- Sex
- Pick the option that matches your situation — the maths changes per option. Choices: Male, Female.
- Hours since first drink
- The hours since first drink used in the calculation. Starts at 2 so you have a working example on load. Accepted range: 0–24.
Results
- Estimated BAC
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Status
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Hours until roughly zero
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Hours until below 0.08%
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Peak BAC before metabolism
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Standard drinks counted
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the blood alcohol content estimator work?
The Widmark formula estimates blood alcohol from body water distribution. It is an estimate only — food, medication, and individual metabolism shift the real number. Never use it to decide whether to drive. The underlying maths is: BAC = (Alcohol grams ÷ (weight g × r)) × 100 − 0.015 × hours.
What do I need to enter?
4 values: standard drinks, body weight, sex, and hours since first drink. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the estimated bac result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
Who is this tool for?
It's built for anyone tracking a health or training target and wanting the standard formula applied correctly, without a signup or an app.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). BAC Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/bac-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/bac-calculator" target="_blank" rel="noopener">BAC Calculator — RevenueLab</a> (2026).</p>
Source: [BAC Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/bac-calculator) (2026).