Blood Alcohol (BAC) Calculator

Get a rough estimate of blood alcohol concentration with the Widmark formula. For education only — never use it to decide whether to drive.

One US standard drink = 12 oz beer (5%), 5 oz wine (12%) or 1.5 oz spirits (40%).

Estimated BAC
0.046 %

Rough estimate only. Food, medications, health and genetics change real BAC a lot. Never use this to decide whether you are safe to drive — if you have been drinking, don’t drive.

Estimated BAC over time%
Estimated BACU.S. driving limit (0.08%)
00.020.040.060.08012345NowHours since first drink
Typical effects
Mild impairment — relaxation, reduced judgment
Time until about 0.00%
3
Pure alcohol consumed
42 g
Show the working
  1. Alcohol = 3 × 14 g = 42 g
  2. Peak BAC = 42 g ÷ (0.68 × 81647 g) × 100 = 0.076%
  3. After 2.0 h: 0.076 − 0.015 × 2.0 = 0.046%

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Formula

BAC (%) = A ÷ (r × W) × 100 − β × tA = grams of alcohol, W = body weight in grams, r = 0.68 (men) or 0.55 (women)β ≈ 0.015 % per hour, t = hours since drinking began

How it works

Important: this calculator gives a rough, population-average estimate for education only. Your actual blood alcohol can be much higher than shown. It must never be used to judge whether you can drive, operate machinery or make any safety decision. The only safe blood alcohol level for driving is zero.

The estimate uses the Widmark formula, developed in the 1930s. It spreads the alcohol you drank through your body water — represented by the factor r, which is lower on average for women because of differences in body composition — and then subtracts the amount your liver typically clears per hour.

Real-world BAC depends on many things the formula ignores: how fast you drank, whether you ate, your liver health, medications and individual metabolism. Absorption takes 30–90 minutes, so BAC can keep rising after your last drink. Most U.S. states set the driving limit at 0.08% (Utah: 0.05%), and commercial drivers and under-21 drivers face stricter limits.

If someone is confused, vomiting, having seizures, breathing slowly or cannot be woken, call emergency services — these are signs of alcohol poisoning. This tool is not medical or legal advice.

Frequently asked questions

Can I speed up sobering up?

No. Coffee, cold showers and exercise do not change how fast your liver removes alcohol. Only time lowers BAC, at roughly 0.015% per hour on average.

Why is the result different for men and women?

At the same weight, women on average have less body water, so the same amount of alcohol produces a higher concentration. The formula reflects this with a smaller r factor.

Is a breathalyzer more accurate?

A calibrated breath test measures your actual alcohol level rather than predicting it, so it is far more reliable than any formula. Consumer devices still vary in accuracy.

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