BAC Calculator — Estimate Your Blood Alcohol Content
Estimate your blood alcohol content based on drinks consumed, weight, sex, and time elapsed. Includes BAC effects by level and important safety information.
Understanding blood alcohol content isn't just for avoiding legal trouble — it's genuinely useful for making informed decisions about when it's safe to drive, operate machinery, or even just go to sleep after a night out. The BAC calculator on CalcHub gives you a rough estimate based on what you've had to drink and a few personal details.
This is an estimate tool, not a breathalyzer. Read the caveats carefully.
How BAC Is Calculated
The most widely used formula is the Widmark formula:
BAC = (Alcohol consumed in grams) ÷ (Body weight in grams × Distribution ratio) × 100The distribution ratio (r) is approximately 0.68 for men and 0.55 for women, reflecting the difference in average body water content. Women typically reach higher BAC levels from the same amount of alcohol because of lower total body water and, on average, lower levels of alcohol dehydrogenase enzyme in the stomach.
The calculator also subtracts metabolized alcohol: the liver processes roughly 0.015–0.017% BAC per hour for most people.
What to Enter in the Calculator
- Number of drinks (use standard drink equivalents)
- Time elapsed since your first drink
- Your weight (pounds or kg)
- Biological sex
BAC Levels and Their Effects
| BAC Level | Typical Effects |
|---|---|
| 0.02–0.03% | Mild relaxation, slight mood lift, minimal impairment |
| 0.05–0.07% | Lowered inhibitions, slight coordination reduction, reduced reaction time |
| 0.08% | Legal driving limit in most US states, Canada, UK, Australia |
| 0.10–0.12% | Slurred speech, noticeably impaired coordination and judgment |
| 0.15–0.20% | Major impairment, significant nausea risk, difficulty walking |
| 0.25–0.30% | Severe impairment, blackout risk, dangerous loss of consciousness possible |
| 0.30–0.40% | Life-threatening; risk of respiratory depression and death |
Why the Estimate Can Be Off
The Widmark formula is a population-average model. Your actual BAC can differ significantly because of:
- Food consumption — a full stomach slows alcohol absorption dramatically; an empty stomach accelerates it
- Drink ABV — craft beers, wine, and cocktails vary widely; the calculator uses standard drink equivalents
- Metabolic rate — varies by genetics, liver health, regular drinking habits, and medications
- Carbonation — carbonated drinks (champagne, sparkling mixers) accelerate absorption
- Hydration status — dehydration concentrates blood alcohol
How long does it take to sober up?
The liver metabolizes alcohol at a roughly fixed rate — approximately one standard drink per hour for most people. There is no method to speed this up. Coffee does not sober you up (it just makes you an alert drunk). Cold showers don't help. Only time reduces BAC.
Can I be over the limit the morning after?
Yes. If you consumed a large amount late at night, your BAC can still be above the legal limit the next morning. A rough check: if you drank more than 4–5 standard drinks and went to sleep within a few hours, there's a reasonable chance you're still over 0.08% when you wake up. The Widmark formula with time-since-first-drink can give you a rough estimate, but when in doubt, don't drive.
Does body weight really affect BAC that much?
Significantly, yes. A 120 lb person and a 220 lb person consuming the same drinks will have substantially different BAC levels — the heavier person has more body water to dilute the alcohol. This is one of the main reasons women, who typically weigh less and have lower body water percentages, are more vulnerable to alcohol effects at the same drink count.
Related Calculators
- Water Intake Calculator — rehydration is important after drinking
- Calorie Calculator — alcohol contributes 7 calories per gram to your daily total
- BMI Calculator — weight affects BAC; check your health metrics here