Understand how alcohol is processed. This free blood alcohol calculator gives a rough educational BAC estimate from your weight, drinks and time — it cannot tell you if you’re safe to drive, and the only safe amount before driving is zero.
⚠ Educational estimate only. This cannot tell you whether you are safe or legal to drive — real BAC depends on many factors this tool can’t capture. The only safe amount of alcohol before driving is zero. Never use this to decide to drive. If you’ve been drinking, do not drive.
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drinks
hrs
A “standard drink” ≈ 14 g of pure alcohol (a 12 oz beer, 5 oz wine or 1.5 oz spirits).
Estimated BAC
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Alcohol consumed
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Standard drinks
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Hours elapsed
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This is a rough estimate, not a measurement. Do not drive after drinking.
BAC varies with food, metabolism, medication, health and more — no formula is reliable for an individual. Legal limits differ by region and many are well below the figures shown. Never rely on this to drive.
This free blood alcohol calculator gives a rough educational estimate of blood alcohol content (BAC) using the Widmark formula. It is for general understanding only and cannot tell you whether you are safe or legal to drive.
Read this first: this tool is educational only. It cannot measure your real BAC or tell you if you’re fit or legal to drive — actual BAC depends on food, metabolism, medication, health and other factors no formula can capture. The only safe amount of alcohol before driving is zero. If you have been drinking, do not drive — arrange a taxi, rideshare, or a sober driver.
What this blood alcohol calculator shows you
A BAC calculator estimates the percentage of alcohol in your bloodstream from your weight, sex, number of standard drinks and time elapsed. It uses the Widmark formula and subtracts a typical elimination rate over time. The result is an approximation for learning how alcohol is processed — not a measurement.
How BAC is estimated
BAC% = (grams of alcohol ÷ (body weight g × r)) × 100 − 0.015 × hours
(r ≈ 0.68 for men, 0.55 for women)
Each “standard drink” is about 14 grams of pure alcohol. The body eliminates roughly 0.015% per hour, which is why time lowers the estimate. Because r and elimination vary between people, two people drinking the same amount can have very different real BAC.
What a standard drink is
Drink
Typical serving
Regular beer (~5%)
12 oz / 355 ml
Wine (~12%)
5 oz / 148 ml
Spirits (~40%)
1.5 oz / 44 ml
Each contains roughly 14 g of pure alcohol. Cocktails and stronger pours can count as more than one.
Why you should never use BAC estimates to drive
It’s an estimate, not a breathalyzer. Your true BAC can be higher than any formula predicts.
Impairment starts before legal limits. Reaction time and judgment are affected at low levels.
Limits vary by region and many are well below the numbers a calculator shows.
The safe choice is simple: if you’ve had any alcohol, don’t drive.
Blood Alcohol Calculator FAQ
How is blood alcohol content estimated?
The Widmark formula divides the grams of alcohol consumed by your body weight times a distribution factor (about 0.68 for men, 0.55 for women), then subtracts roughly 0.015% per hour for elimination. It's an approximation, not a measurement.
Can this tell me if I'm okay to drive?
No. It cannot. Real BAC varies with food, metabolism, medication and health, and impairment begins below legal limits. The only safe amount of alcohol before driving is zero — if you've been drinking, don't drive.
What is a standard drink?
About 14 grams of pure alcohol — roughly a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits. Strong cocktails and large pours can count as more than one.
How long does alcohol take to leave your system?
The body eliminates alcohol slowly, around 0.015% BAC per hour, and only time lowers it — coffee, food or a cold shower don't speed it up. After drinking, it can take many hours to return to zero.
Why can two people have different BAC from the same drinks?
Body weight, sex, body composition, food, hydration, medication and individual metabolism all affect BAC. That's a key reason no calculator can reliably tell any individual their true level.
Is the blood alcohol calculator free to use?
Yes, this BAC calculator is completely free and gives an instant educational estimate in your browser. It is not a substitute for a breathalyzer or professional judgment.
