Blood Alcohol Calculator
Estimate blood alcohol concentration with the Widmark equation from body weight, drinks and time elapsed, with an editable r factor and elimination rate.
Never use this to decide whether you are safe to drive. The Widmark equation is a rough population average and a real breath or blood test can read far higher. If you have been drinking, do not drive.
Estimated blood alcohol concentration
0.052%
after 2 h, from a peak of 0.082% at the moment everything was absorbed.
BAC = 42.0 g ÷ (75,000 g × 0.68) × 100 − 0.015 × 2.00 = 0.052%
Time until you drop below common driving limits
| Limit | Where it applies | Estimated time from now |
|---|---|---|
| 0.08% | United States (most states), Canada, England & Wales | Already below |
| 0.05% | Scotland, most of the EU, Australia, South Africa | 9 min |
| 0.02% | Sweden, Norway, Poland, many novice-driver rules | 2 h 9 min |
| 0.00% | Zero-tolerance jurisdictions and most professional drivers | 3 h 29 min |
These are estimates from a formula, not a legal defence, and the limits listed are the common ones — check your own jurisdiction. Nothing but time lowers BAC: coffee, food, cold showers and exercise do not speed up the roughly 0.015 %/hour your liver manages.
BAC hour by hour
A rough estimate only, not medical or legal advice, and not a substitute for a breathalyser. Widmark's 1932 equation assumes instant absorption, a single average distribution factor and a fixed elimination rate, so it can easily be 20–40% out for any one person. Food in the stomach, sex, age, body composition, liver health, medication, carbonation and how fast you drank all shift the real number, and this model gives the peak immediately rather than the 30–90 minutes absorption really takes. Alcohol impairs driving well below any legal limit — if you have been drinking, do not drive.
What is the Blood Alcohol Calculator?
The Widmark equation estimates BAC as the grams of alcohol consumed divided by body mass in grams times a distribution factor r, multiplied by 100, minus the elimination rate (about 0.015% per hour) times the hours elapsed.
- Widmark equation with both r and the elimination rate exposed as editable inputs
- Standard drink counting for the US, UK, Australia, Canada and Germany, or itemised volume and ABV entry
- Peak BAC, current BAC and estimated time back to zero
- Time until you fall below the 0.08, 0.05, 0.02 and 0.00 limits used around the world
- Hour-by-hour BAC chart colour-coded against those limits
- Runs completely offline — nothing about your drinking leaves your device
How to use the Blood Alcohol Calculator
- 1
Enter your body weight in kilograms or pounds and pick your sex, which presets the Widmark r factor.
- 2
Adjust r and the elimination rate if you have better figures than the population defaults.
- 3
Say how many hours have passed since your first drink.
- 4
Choose to enter a number of standard drinks on your country's definition, or itemise each drink by volume and ABV.
- 5
Read the current and peak BAC, the hours to reach zero, and the table of times until you drop below each common limit.
About the Blood Alcohol Calculator
The ByteTools Blood Alcohol Calculator applies Widmark's 1932 equation to your own figures. Enter your body weight, how much you have drunk and how long ago you started, and it returns the peak BAC, the current estimate, and how long the model says it takes to fall back to zero and below common driving limits.
Both of the constants Widmark chose are editable rather than hidden. The distribution factor r defaults to 0.68 for men and 0.55 for women but moves with body composition, and the elimination rate defaults to 0.015% per hour while published values range from about 0.010 to 0.020. Drinks can be entered as a count of standard drinks on five national definitions, or itemised by volume and ABV.
Everything runs locally in your browser and nothing is uploaded. This is a rough estimate only, never a legal defence and never a substitute for a breathalyser. Widmark's model can be 20 to 40% out for any one person, and alcohol impairs driving well below any legal limit — if you have been drinking, do not drive.
Frequently asked questions
What is the Widmark formula for BAC?
BAC as a percentage equals the grams of alcohol consumed divided by (body mass in grams × r), multiplied by 100, then minus the elimination rate × hours elapsed. For a 68 kg man who drinks three US standard drinks — 42 g of ethanol — that is 42 ÷ (68,000 × 0.68) × 100, or about 0.091% before any elimination.
How long does it take for alcohol to leave your system?
At the usual 0.015% per hour, a BAC of 0.09% takes about six hours to reach zero. Nothing speeds that up: coffee, food, cold showers, exercise and sleep all change how you feel without changing how fast your liver clears alcohol.
How accurate is a BAC calculator?
Not accurate enough to rely on. Widmark's model assumes instant absorption, one average distribution factor and a fixed elimination rate, so real readings routinely land 20 to 40% away from it. Food in the stomach, age, body composition, liver health, medication, carbonation and drinking speed all move the true number.
What is the r factor in the Widmark equation?
It is the ratio of your body water to your total body mass, since alcohol distributes into water rather than fat. Widmark's original values were 0.68 for men and 0.55 for women. Leaner bodies sit higher and higher body fat lower, which is why the field is editable here.
Can I use this to decide whether to drive?
No — and please do not. This is a population average from a 1932 formula, not a measurement of your blood, and it does not know what you actually drank or when. Driving impairment begins well below every legal limit. If you have been drinking, do not drive.
Is my input stored anywhere?
No. Every calculation happens in JavaScript in your browser. Nothing about your weight, drinks or timing is uploaded, logged or saved, and the tool works offline.
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