BAC Calculator
Estimate your blood alcohol content based on your weight, gender, number of drinks, and time elapsed since you started drinking.
BAC Impairment Levels Reference
| BAC Level | Stage | Effects |
|---|---|---|
| 0.02–0.04% | Mild | Relaxation, slight mood lift |
| 0.05–0.07% | Moderate | Reduced inhibition, slower reaction |
| 0.08% | Legal limit | Impaired balance, judgment, vision |
| 0.10–0.12% | Significant | Slurred speech, poor coordination |
| 0.15–0.20% | Severe | Nausea, disorientation, memory gaps |
| 0.25%+ | Dangerous | Blackout, alcohol poisoning risk |
This calculator provides estimates only. Never drive after drinking. If you or someone else is in danger, call 911.
Frequently Asked Questions
What is BAC and how is it calculated?
Blood Alcohol Content (BAC) is the percentage of alcohol in your bloodstream. A BAC of 0.08% means 0.08 grams of alcohol per 100 mL of blood. This calculator uses the Widmark formula: BAC = (drinks × 14g × 5.14) / (weight_lbs × r) − (0.015 × hours), where r is the Widmark factor (0.73 for men, 0.66 for women — accounts for different body water distribution). One standard drink = 14 grams of pure alcohol = 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%).
What is the legal BAC limit for driving?
In all 50 US states, the legal BAC limit for driving is 0.08%. Utah has the strictest limit at 0.05%. Commercial drivers are held to 0.04%. Drivers under 21 face a 0.00–0.02% limit in most states (zero-tolerance). Many countries outside the US have stricter limits: 0.05% in most of Europe, Australia, and Canada. 0.03% in Japan. 0.00% in some Nordic countries. At 0.08% BAC, crash risk is 4× higher than sober. At 0.15%, it is 12× higher. Never drive if you have been drinking.
How long does alcohol stay in your system?
Your body eliminates alcohol at approximately 0.015% BAC per hour, regardless of drinking coffee, eating, sleeping, or exercising — these are myths that do not speed elimination. To be completely sober: divide your peak BAC by 0.015. Example: if you reach 0.12% BAC, it takes approximately 8 hours to reach 0.00%. For a breath or blood test, alcohol is detectable for up to 24 hours. For urine tests (EtG), detection can extend to 72–80 hours. This calculator gives an estimate only — individual metabolism varies significantly.
What factors affect BAC besides weight and drinks?
Many factors influence BAC beyond the basic Widmark formula: Food: eating slows alcohol absorption significantly — drinking on an empty stomach can raise peak BAC by 50% vs. eating a full meal. Carbonation: sparkling wine and mixers may speed absorption. Medications: some drugs dramatically potentiate alcohol (benzodiazepines, opioids, antihistamines, sleep aids). Fatigue: impairs judgment at lower BAC levels. Tolerance: regular drinkers may feel less impaired at a given BAC but their measured impairment on reaction tests is the same. Hydration: alcohol is a diuretic; dehydration worsens effects.