BAC Calculator
Estimate your blood alcohol content based on gender, weight, number of drinks, and time elapsed.
Important Disclaimer
This calculator is for educational purposes only. It provides a rough estimate and should never be used to determine whether you are fit to drive, operate machinery, or perform any activity that requires sobriety. Actual BAC depends on many individual factors not accounted for here. When in doubt, do not drive.
1 standard drink = Beer (12 oz / 5% ABV) = ~14g of alcohol
Last updated: April 8, 2026· Reviewed by the CalcNeeds Team
About This Calculator
This BAC calculatorestimates your blood alcohol content based on how many drinks you've had, your weight, your sex, and the time elapsed since you started drinking. It uses the Widmark formula— the same equation used by forensic toxicologists, court systems, and most BAC apps. Enter your numbers and you'll get an instant estimate of where your BAC stands relative to common legal limits.
Important: this is an estimate, not a measurement. Real BAC varies based on factors no calculator can know — your metabolism, food in your stomach, medications, hydration, liver function, and dozens of others. Never use a calculator to decide whether you're safe to drive.If you've been drinking, get a ride.
How the Widmark formula works
The Widmark formula, developed by Swedish chemist Erik Widmark in the 1930s, is the foundation of nearly every BAC calculation in use today. The simplified version is:
BAC = (alcohol grams ÷ (body weight in g × r)) × 100 − (0.015 × hours)
ris the "Widmark factor" — the fraction of body mass that's water and can hold alcohol. It averages 0.68 for males and 0.55 for females. The lower factor for females reflects, on average, a higher proportion of body fat (which doesn't absorb alcohol) — meaning the same amount of alcohol produces a higher BAC in a female of the same weight as a male.
A standard U.S. drink contains 14 grams of pure ethanol— that's a 12 oz beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 80-proof spirits. Stronger drinks count as more than one standard drink.
The body eliminates alcohol at roughly 0.015% BAC per hour, regardless of weight or sex. This is the "− 0.015 × hours" term — it subtracts off whatever your liver has burned through since you started drinking.
Legal BAC limits in the United States
0.08% — DUI/DWI limit (49 states + DC). Per se illegal to drive at or above this level for drivers age 21+.
0.05% — Utah only. Utah lowered its limit to 0.05% in 2018, the lowest in the nation.
0.04% — Commercial drivers (CDL). Federal law applies a stricter 0.04% limit to anyone operating a commercial vehicle.
0.02% or any detectable amount — Drivers under 21.All 50 states have "zero tolerance" laws for drivers under the legal drinking age.
Many states also have an enhanced "aggravated DUI" threshold at 0.15% or 0.16% with much harsher penalties. And you can be charged with impaired driving below 0.08% if an officer observes impairment — the limit is a per-se threshold, not a safe-to-drive line.
Factors that affect your real BAC
The Widmark formula is a simplification. In reality, dozens of factors push your actual BAC above or below the calculated estimate:
Food in your stomach: drinking on an empty stomach can produce a peak BAC up to 2× higher than the same drinks with a full meal. Food slows alcohol absorption.
Drinking speed: downing 4 drinks in an hour produces a much higher peak than spreading them over 4 hours, even though the total alcohol is the same.
Body composition:two people with the same weight but different body fat percentages will have different BACs. Lean tissue holds water (and alcohol); fat doesn't.
Hydration, medications, sleep, stress, illness— all push BAC unpredictably in either direction.
Tolerance does NOT lower BAC.Regular drinkers may feel less impaired at a given BAC, but their blood alcohol level is still the same. They're just as illegal to drive.
How long does alcohol stay in your system?
At the elimination rate of ~0.015% per hour, alcohol clears predictably:
BAC of 0.04% → fully sober in ~3 hours
BAC of 0.08% → fully sober in ~5–6 hours
BAC of 0.16% → fully sober in ~10–11 hours
Note that nothing accelerates this process. Coffee, cold showers, exercise, drinking water, vomiting, greasy food — none of them lower your BAC. They might make you feel more alert, but your blood alcohol stays exactly where the math says it is. Only time (and your liver) sobers you up.
Frequently Asked Questions
How is blood alcohol content calculated?
BAC is calculated with the Widmark formula: BAC = (alcohol in grams ÷ (body weight in grams × Widmark factor)) × 100 − (0.015 × hours since drinking started). The Widmark factor is 0.68 for males and 0.55 for females. The 0.015 term accounts for the body's natural alcohol elimination rate of about 0.015% BAC per hour.
What's the legal BAC limit to drive?
0.08% in 49 U.S. states and DC for drivers 21 and over. Utah is 0.05%. Commercial drivers are limited to 0.04%. Drivers under 21 have zero tolerance — any detectable alcohol is illegal. Many states also have aggravated-DUI thresholds at 0.15%–0.16% with much harsher penalties.
How many drinks until I'm at 0.08?
It depends heavily on weight, sex, and time. As rough averages: a 160-lb male reaches 0.08 after about 4 standard drinks in 1 hour. A 140-lb female reaches it after about 3 standard drinks in 1 hour. Use the calculator above for your specific weight, sex, and timing — and remember the answer is an estimate, not a guarantee of legal sobriety.
How long does alcohol stay in your system?
Your body eliminates alcohol at roughly 0.015% BAC per hour regardless of weight, sex, or what you do. A BAC of 0.08 takes about 5–6 hours to clear; a BAC of 0.16 takes 10–11 hours. Coffee, cold showers, food, water, and exercise do NOT speed this up — only time does.
Does food slow alcohol absorption?
Yes, significantly. Drinking on an empty stomach can produce a peak BAC up to 2× higher than the same drinks consumed with a full meal. Food slows the rate at which alcohol passes from your stomach into your bloodstream, lowering the peak. It does not change the total amount of alcohol you absorb — just spreads it over more time.
Does this calculator account for tolerance?
No — and neither does any other BAC calculator. Tolerance affects how impaired you feel at a given BAC, not the BAC itself. A heavy drinker and a light drinker with the same BAC are both equally illegal to drive, even if one feels fine and the other can't stand up. BAC is a chemical measurement, not a feeling.
Can I beat a breathalyzer?
No. Mints, mouthwash, holding your breath, hyperventilating, and the other folk tricks don't work — modern evidential breathalyzers correct for or detect almost all of them. Some mouthwashes contain alcohol that can briefly inflate a reading; police are trained to wait 15+ minutes before testing to clear this. The only reliable way to pass a breathalyzer is to be sober.
Why is the BAC limit lower for women?
It isn't — the legal BAC limit (0.08%) is the same for everyone. But women generally reach a given BAC with less alcohol than men of the same weight. This is because the average female body has a higher proportion of fat (which doesn't hold alcohol) and a lower proportion of water than the average male body. The Widmark factor (0.55 for females vs 0.68 for males) reflects this average physiological difference.
Is this calculator accurate enough to decide if I can drive?
Absolutely not. The Widmark formula is a population average — your individual BAC can vary by 30%–50% above or below the calculated value depending on metabolism, food, medications, and dozens of other factors. Use this tool for education only. If you've been drinking, the only safe choice is to not drive: call a rideshare, take a taxi, or ask a sober friend.
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