Estimate your blood alcohol content from drinks, weight and time.
An estimate only — never use it to decide whether to drive.
How is blood alcohol content (BAC) calculated?
Using the Widmark formula, BAC% = (alcohol grams ÷ (body weight in grams × r)) × 100 − 0.015 × hours, where r is 0.68 for men and 0.55 for women. BAC falls about 0.015% per hour as your body clears alcohol. A 180 lb man with 4 drinks over 2 hours is roughly 0.07% BAC. Food, medication and health affect the true figure.
Understanding your result
BAC falls by about 0.015% per hour as your body clears alcohol. This is a rough estimate: food, medication, health and the real strength of each drink all change the true figure.
Formula and method
BAC% = (alcohol grams ÷ (body weight in grams × r)) × 100 − 0.015 × hours, where r is 0.68 for men and 0.55 for women.
Assumptions and limitations
This is an estimate only and must never be used to decide whether it is safe or legal to drive. The Widmark formula ignores food, medication, health, tolerance and the true strength of each drink, so your real BAC may be much higher. It is not medical or legal advice; if you have been drinking, do not drive.
Worked example
A 180 lb man who has had 4 standard drinks over 2 hours is at roughly 0.07% BAC — close to, but under, the 0.08% limit.
How to use this tool
- Choose your sex and enter your body weight.
- Enter the number of standard drinks.
- Enter the hours since your first drink, then press Estimate.
About the Blood Alcohol (BAC) Calculator
The Blood Alcohol (BAC) Calculator estimates your blood alcohol content using the Widmark formula, based on your drinks, weight, sex and the time since your first drink.
Who should use this tool
Adults curious about roughly how alcohol may affect their blood alcohol content, given drinks, weight, sex and time, using the Widmark formula. Intended purely for general educational awareness of how quickly the body processes alcohol, never as a measure of fitness to do anything.
Benefits
- Illustrates how drinks, weight and time affect estimated BAC
- Shows the body clearing alcohol gradually over hours
- Uses the widely known Widmark formula
- Keeps your details on your own device, not a server
Practical use cases
- Learning how alcohol is processed over time
- Understanding why BAC falls slowly, not instantly
- Seeing how weight and sex change the estimate
- General educational awareness of drinking and the body
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Frequently asked questions
Is it safe to drive under 0.08%?
No. Impairment begins well below 0.08%, limits are lower in many places, and this is only an estimate. If you have been drinking, do not drive.
How long until I am sober?
The tool estimates the hours for your BAC to return to zero at about 0.015% per hour, but only time clears alcohol — coffee and cold showers do not.
Why can my real BAC differ from this estimate?
The Widmark formula uses average factors and cannot account for food in your stomach, medications, your health, tolerance or the actual alcohol content of each drink. Any of these can push your true BAC well above or below the figure shown. For this reason the result is only a rough illustration.
Can I use this to decide when to drive?
No. This tool must never be used to judge whether you are safe or legal to drive. It is an estimate that can be far from your real level, and impairment can occur below any legal limit. If you have consumed alcohol, the only safe choice is not to drive.