Blood alcohol estimate
Widmark estimate and theoretical delays — never a green light to drive.
- Instant
- Free
- Private (processed locally)
- No sign-up
Understand BAC — without ever turning it into a licence to drive
The Widmark formula, used in forensic medicine since 1932, gives an order of magnitude for blood alcohol. This tool applies it purely for education: to see the effect of one more drink, or how many hours it takes to come back down. Never to decide whether to drive.
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Enter sex and weight
They determine the alcohol distribution volume.
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Enter drinks and time
1 standard drink = 10 g of pure alcohol.
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Read the estimate
Approximate BAC and theoretical delays to drop below the thresholds.
What a standard drink looks like (10 g of alcohol)
| Drink | Volume | ABV |
|---|---|---|
| Beer | 25 cl | 5% |
| Wine | 10 cl | 12% |
| Spirits | 3 cl | 40% |
| Aperitif (port…) | 7 cl | 18% |
⚠️ A theoretical estimate with a wide margin of error. The only result that counts behind the wheel is the breathalyser’s. When in doubt, don’t drive: call someone, take a taxi or sleep it off. Alcohol is involved in roughly one in four road deaths.
Frequently asked questions
How does the Widmark formula work?
BAC = grams of alcohol / (weight × r), where r is the distribution coefficient (0.68 for men, 0.55 for women, because fat mass holds less water). Then the eliminated alcohol is subtracted: about 0.15 g/L per hour.
Why is this estimate so unreliable?
It ignores a host of real factors: alcohol drunk on an empty stomach or not, your personal elimination rate (which varies from 0.10 to 0.20 g/L/h), your metabolism, your medication, your fatigue. The gap with reality can reach 30%.
How long to eliminate the alcohol?
The body clears about 0.15 g/L per hour, and nothing speeds it up: not coffee, not a cold shower, not exercise, not water. Only time lowers BAC. After a heavy night, alcohol may still be present the next morning.
Can I rely on it to know whether I can drive?
No, never. No estimate replaces a breathalyser, and when in doubt the only responsible answer is not to drive. The legal limit is often 0.5 g/L (0.2 g/L for young drivers in several countries), but accident risk rises from the very first drink.