WiseCalcs

BAC calculator

Enter the number of standard drinks, your body weight, your sex, and the hours since your first drink. The calculator gives a rough Widmark estimate of blood alcohol concentration. It is not accurate enough to decide whether to drive.

Use it to understand roughly how alcohol affects BAC — never to judge fitness to drive.

kg
h

Estimated BAC

0.04%

Alcohol
30 g
Hours to sober
2.7 h

The result updates as you type. The headline is the estimated BAC; the others show grams of alcohol and a rough time until it clears. Real values vary widely.

How does it work?

This is an estimate. Real BAC varies with food, drink strength, metabolism, and timing. Never use it to decide whether to drive — the only safe amount before driving is none.

Widmark BAC formula

BAC=AW×r×100−0.015 t\text{BAC} = \frac{A}{W \times r}\times 100 - 0.015\,t
BAC
Blood alcohol concentration in percent.
A
Grams of pure alcohol (10 g per standard drink).
W
Body weight in grams.
r
Distribution factor: 0.68 male, 0.55 female.
t
Hours since the first drink.

Three drinks (30 g) for an 80 kg man after 1 hour: 30 / (80000 × 0.68) × 100 − 0.015 = about 0.04%.

Method & sources

Blood alcohol is estimated with the Widmark formula from standard drinks, weight, sex, and elapsed time. The historical Widmark reference below documents the method. This is an educational estimate only — never use it to decide whether you can drive.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

How we calculate

  • Uses the Widmark formula with 10 g of alcohol per standard drink.
  • Distribution factor is 0.68 for men and 0.55 for women.
  • Alcohol is eliminated at about 0.015% per hour.
  • This is a rough estimate, not a legal or medical measurement.

Rounding

BAC is shown to three decimals. The calculation uses full precision.

What this calculator does

The Widmark formula estimates blood alcohol concentration from the alcohol consumed, body weight, sex, and time. This calculator applies it to give a rough percentage. It is an educational estimate only and must never be used to decide whether you can legally or safely drive.

How to use it

  1. Enter the number of standard drinks (10 g of alcohol each).
  2. Enter your body weight.
  3. Pick your sex, which sets the distribution factor.
  4. Enter the hours since your first drink.

A worked example

Three standard drinks (30 g) for an 80 kg man after one hour gives roughly 0.04%. The same drinks for a lighter person, or a woman, would estimate higher.

Why it can't tell you to drive

Actual BAC depends on food, drink strength, how fast you drank, medication, hydration, and individual metabolism — none fully captured here. The only safe amount of alcohol before driving is none.

Common mistakes

  • Assuming a 'standard drink' matches your actual glass or measure.
  • Treating the estimate as a legal reading.
  • Using it to justify driving — never do this.

When it's useful

For general awareness of how drinks, weight, and time affect alcohol levels — purely educational, never a green light to drive.

FAQ

Can I use this to decide whether to drive?
No. It is a rough estimate and ignores many factors. The only safe choice before driving is to not drink at all.
What is a standard drink?
Here it is 10 g of pure alcohol — roughly a small beer, a small glass of wine, or a single spirit measure. Real drinks vary.
Why do men and women get different results?
Body water differs on average, so the Widmark distribution factor is 0.68 for men and 0.55 for women.
How fast does alcohol leave the body?
Roughly 0.015% per hour, but this varies by person. The 'hours to sober' figure is only a guide.
Is the estimate accurate?
No — it can be off in either direction. Food, drink strength, timing, and metabolism all change real BAC.
Can I share a calculation?
Yes. Use Share to copy a link that reopens the calculator with the same inputs.

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