Blood Alcohol Content (BAC) Calculator

BAC is the percentage of alcohol in your bloodstream by volume — and it's the single number that determines whether you're legally drunk, how impaired your judgment is, and when it's safe to drive. The problem is that BAC is invisible. You can feel fine at 0.06% and already be significantly impaired. You might feel drunk at 0.05% the first time you drink and not feel it until 0.09% after years of tolerance. The BAC calculator gives you the number behind the feeling — so you can make decisions based on facts, not guesswork.

How Your BAC Is Calculated — the Widmark Formula

The standard formula used in forensic toxicology for over 90 years:

BAC = (A × 5.14 / W × r) − 0.015 × H

Where A = total grams of alcohol consumed, W = body weight in pounds, r = Widmark factor (0.73 for men, 0.66 for women — reflects body water percentage), H = hours since first drink. The elimination rate of 0.015% per hour is the average; individual rates range from 0.010% to 0.020%.

One standard drink = 14 grams of pure alcohol = 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%). Getting this baseline right matters — a craft IPA at 8% in a pint glass is actually 2.7 standard drinks, not one. Use this online calculator with your actual numbers. The ABV calculator helps you count standard drinks from any beverage.

BAC Levels and What They Actually Mean

The numbers tell a more complicated story than the legal limit suggests:

• 0.02–0.03%: subtle mood elevation, slight relaxation. Some studies show measurable impairment in divided-attention tasks even here.
• 0.05%: reduced alertness, impaired judgment, slower reaction time. Crash risk roughly double sober. Legal in some countries, above limit in others.
• 0.08%: the US legal limit for driving. Marked coordination problems, significant reaction time increase, reasoning impaired. Crash risk is 7× sober at this level.
• 0.10–0.15%: slurred speech, significant balance issues, major reaction time impairment. Many people still believe they're "fine."
• 0.20–0.25%: disorientation, nausea, need assistance walking. Risk of aspiration if vomiting.
• 0.30%+: loss of consciousness, respiratory depression risk. Medical emergency territory.

Why Two People Drinking the Same Amount Have Different BAC

Body weight is the biggest variable — a 130-lb person reaches double the BAC of a 260-lb person from the same drinks. But beyond weight, biological sex matters significantly: women have lower average body water percentage (which is why the Widmark r-factor is lower) and typically lower levels of alcohol dehydrogenase in the stomach lining, meaning more alcohol enters the bloodstream unmetabolized. Food slows alcohol absorption dramatically — a full meal can reduce peak BAC by 20–30% and delay it by 30–60 minutes. Fatigue, medications, and individual enzyme genetics all add further variation. The alcohol by volume calculator and toxicology calculators provide related tools.

How Long Until You're Sober Enough to Drive?

Time is the only reliable method — no amount of coffee, water, food, or cold showers speeds up alcohol metabolism. Your liver processes alcohol at a fixed rate of roughly 0.015% per hour (one standard drink per hour for an average person). To estimate when you'll be under the legal limit: Time to sober = (BAC − 0.08) / 0.015 hours. At 0.14% BAC: (0.14 − 0.08) / 0.015 = 4 hours minimum until legal. But "legal" is not the same as "unimpaired" — research shows measurable cognitive effects persist well below 0.08%. The safest rule: if you've been drinking, don't drive until you've slept and the math clearly puts you at 0.00%.