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Blood Alcohol Calculator

Estimate BAC with the Widmark formula.

Best for: Use it for general education about how alcohol is processed — not to judge fitness to drive or operate machinery.

Complete guide
Why this result happened View assumptions
Country (units):

Input

How it's calculated & sources
The Blood Alcohol Calculator uses the standard formula for this calculation. It runs entirely in your browser, so your inputs are never uploaded. Figures are educational estimates, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.
Key assumptions
  • Widmark formula
  • An estimate - never use it to decide whether to drive

Educational estimate only — not medical advice. Consult a qualified healthcare professional for decisions about your health.

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

How it works

Widmark: BAC = (alcohol g × 100) / (weight g × r) − (0.015 × hours)

r = 0.68 (M), 0.55 (F). 1 standard drink ≈ 14 g alcohol.

Example

3 standard drinks, 70 kg male, 2 hours → BAC ≈ 0.058%.

Frequently asked questions

Is this medically reliable?+

No — for educational use only. Never drive after drinking, regardless of any estimate.

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Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is Blood Alcohol?
A blood alcohol concentration (BAC) calculator gives a rough estimate of your BAC from the alcohol consumed, your body weight and sex, and the time elapsed, using the Widmark formula.
Why does Blood Alcohol matter?
It feeds BMI, calorie, body-fat and dosing calculations.
How is Blood Alcohol calculated?
It converts your drinks to grams of alcohol, divides by your body water (weight × a distribution factor, ~0.68 for men and ~0.55 for women), then subtracts the alcohol your body metabolises over time (about 0.015% per hour). Formula: BAC ≈ (alcohol grams ÷ (weight_g × r)) × 100 − (0.015 × hours).
What is a good blood alcohol?
In most U.S. states the legal driving limit is 0.08% BAC (lower for commercial and under-21 drivers); many countries set 0.05% or lower. Impairment begins well below any legal limit.
What are common blood alcohol mistakes?
Treating the estimate as accurate — individual variation is large.
When should you use the Blood Alcohol Calculator?
Use it for general education about how alcohol is processed — not to judge fitness to drive or operate machinery.

What is the Blood Alcohol Calculator?

A blood alcohol concentration (BAC) calculator gives a rough estimate of your BAC from the alcohol consumed, your body weight and sex, and the time elapsed, using the Widmark formula.

How the Blood Alcohol Calculator works

It converts your drinks to grams of alcohol, divides by your body water (weight × a distribution factor, ~0.68 for men and ~0.55 for women), then subtracts the alcohol your body metabolises over time (about 0.015% per hour).

BAC ≈ (alcohol grams ÷ (weight_g × r)) × 100 − (0.015 × hours)

Understanding the inputs

What each value means, why it matters, and a typical range — so you can fill in the calculator with confidence.

Weight

Your body weight, entered in kilograms or pounds.

Why it matters:
It feeds BMI, calorie, body-fat and dosing calculations.
Typical range:
Varies by person; tools accept metric or imperial.
How it affects results:
  • Higher: Raises BMI and calorie needs.
  • Lower: Lowers BMI and calorie needs.

Common mistake: Mixing units - entering pounds where kilograms are expected.

What impacts results most

  1. 1.
    Number of drinks (High impact)More alcohol raises BAC.
  2. 2.
    Body weight (High impact)More body water dilutes alcohol.
  3. 3.
    Time since first drink (High impact)The body clears alcohol over time.
  4. 4.
    Sex (Medium impact)Affects body-water distribution.

Key assumptions

  • Widmark formula
  • An estimate - never use it to decide whether to drive

What's a typical value?

In most U.S. states the legal driving limit is 0.08% BAC (lower for commercial and under-21 drivers); many countries set 0.05% or lower. Impairment begins well below any legal limit.

Estimated peak BAC by standard drinks and body weight (men, before metabolism)

10.034%0.027%0.023%
20.069%0.055%0.046%
30.103%0.082%0.069%
40.137%0.110%0.092%
50.172%0.137%0.114%

Worked example

One U.S. standard drink contains about 14 g of alcohol. Several drinks in a short time can push BAC over legal limits — the only safe driving BAC is zero.

Common mistakes to avoid

  • Treating the estimate as accurate — individual variation is large.
  • Assuming coffee, water or food 'sober you up' faster (only time lowers BAC).
  • Using any BAC estimate to decide to drive.

Reviewed sources & methodology

Methodology: Professional Estimate · Last reviewed June 2026.

Keywords: bac, alcohol, widmark.

This tool is for general information only and is not medical advice. Consult a qualified healthcare professional for decisions about your health.

Sources: U.S. NHTSA — Drunk driving

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the Blood Alcohol Calculator free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the Blood Alcohol Calculator?+

Blood Alcohol Calculator uses the standard blood alcohol formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The Blood Alcohol Calculator runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the Blood Alcohol Calculator on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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Estimate BAC with the Widmark formula.

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The fastest way is to use a free in-browser blood alcohol calculator: https://freetoolsgalaxy.com/tools/blood-alcohol-calculator. Estimate BAC with the Widmark formula.

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