Estimate blood alcohol content using the Widmark formula. See BAC effects by level, US legal limits by state, and how long to sober up | Calculator4U
Estimate blood alcohol level.
A blood alcohol content (BAC) calculator estimates the percentage of alcohol in your bloodstream based on the number of standard drinks consumed, your body weight, biological sex, and time elapsed — using the Widmark formula, the internationally accepted method used by forensic toxicologists, law enforcement, and medical researchers. BAC is expressed as a percentage: 0.08% means 0.08 grams of alcohol per 100 mL of blood. In all 50 US states, 0.08% is the legal driving impairment threshold for adults 21 and older — Utah tightened this to 0.05% in 2019, the strictest limit in the nation.
The Widmark formula: BAC = (Alcohol consumed in grams ÷ (Body weight in kg × r)) × 100 − (0.015 × hours elapsed). The gender distribution constant r = 0.68 for males and 0.55 for females, reflecting the fact that women have proportionally less body water than men of the same weight, producing higher alcohol concentration from identical consumption. One US standard drink contains exactly 14 grams of pure alcohol — equivalent to 12 oz of regular beer (5% ABV), 5 oz of wine (12% ABV), or 1.5 oz of spirits (40% ABV). A 16 oz craft beer at 8% ABV equals approximately 2.13 standard drinks — the single most common miscounting error US drinkers make.
| Body Weight | 2 Drinks (1 hr) | 4 Drinks (2 hrs) | 6 Drinks (3 hrs) |
|---|---|---|---|
| 120 lbs (M) | 0.054% | 0.077% | 0.101% |
| 120 lbs (F) | 0.082% | 0.133% | 0.184% |
| 160 lbs (M) | 0.038% | 0.055% | 0.073% |
| 160 lbs (F) | 0.059% | 0.088% | 0.117% |
| 200 lbs (M) | 0.028% | 0.040% | 0.053% |
| 200 lbs (F) | 0.044% | 0.063% | 0.082% |
Red values exceed 0.08% US legal driving limit. All values are estimates — individual variation is ±20–30%.
| Driver Category | Legal BAC Limit | Notes |
|---|---|---|
| Adults 21+ (all states) | 0.08% | Nationwide standard |
| Adults 21+ (Utah only) | 0.05% | Strictest US state limit since 2019 |
| Commercial drivers (CDL) | 0.04% | All 50 states — FMCSA federal requirement |
| Drivers under 21 | 0.00–0.02% | Zero-tolerance laws in most states |
| School bus / daycare drivers | 0.00% | Absolute zero in most states |
The liver metabolizes alcohol at a fixed average rate of 0.015% BAC per hour — this cannot be accelerated by coffee, food, exercise, cold showers, or any other method. Only time sobers you up. At a starting BAC of 0.10%, complete elimination takes approximately 6.7 hours. At 0.15%, approximately 10 hours. Never estimate sobriety — if in doubt, do not drive.
Important disclaimer: This calculator provides mathematical estimates using average population parameters. Individual BAC varies by up to ±20–30% based on metabolic rate, medications, health conditions, and food intake. This tool is for educational and harm-reduction purposes only and must never be used to determine whether it is safe to drive. The only safe driving decision is zero alcohol consumed.
BAC is calculated using the Widmark formula: BAC = (Alcohol consumed in grams ÷ (Body weight in kg × r)) × 100 − (0.015 × hours elapsed). The gender constant r = 0.68 for males and 0.55 for females, reflecting differences in body water distribution. One US standard drink = 14 grams of pure alcohol (12 oz beer at 5%, 5 oz wine at 12%, or 1.5 oz spirits at 40%). BAC decreases by approximately 0.015% per hour as the liver metabolizes alcohol. Example: a 160 lb man consuming 3 drinks over 2 hours: BAC = (42 ÷ (72.6 × 0.68)) × 100 − 0.030 = 0.085 − 0.030 = 0.055%.
The legal BAC limit for driving in 49 US states is 0.08% for drivers aged 21 and over. Utah has the strictest limit at 0.05% for all adult drivers since 2019. Commercial vehicle drivers (CDL holders) face a federal limit of 0.04% in all 50 states (FMCSA requirement). Zero-tolerance laws apply to drivers under 21 in most states — typically 0.00–0.02%. School bus and daycare vehicle drivers face absolute zero limits in most states. The NHTSA reports alcohol-impaired driving causes approximately 13,500 deaths annually in the US — about 37% of all traffic fatalities.
The liver metabolizes alcohol at a fixed rate of approximately 0.015% BAC per hour — one standard drink per hour for most adults. This rate cannot be increased by coffee, food, cold showers, exercise, or any other method. Only time eliminates alcohol. Approximate time to reach 0.00% BAC from common starting levels: 0.05% = 3.3 hours; 0.08% = 5.3 hours; 0.10% = 6.7 hours; 0.15% = 10.0 hours; 0.20% = 13.3 hours. These are averages — individual metabolic rates vary by ±20–30% based on liver enzyme levels, body composition, medications, and health status. Never estimate sobriety — if in doubt, do not drive.
Food does not lower BAC or speed up alcohol elimination — but it significantly slows alcohol absorption from the stomach into the bloodstream, producing a lower peak BAC from the same number of drinks. Eating a substantial meal before or while drinking can reduce peak BAC by 20–30% compared to drinking on an empty stomach. High-fat, high-protein foods slow gastric emptying most effectively. However, once alcohol is already in your bloodstream, food has no effect — the liver processes it at the same 0.015% per hour regardless. The practical implication: eating before drinking prevents rapid intoxication but cannot sober you up once you are drunk.
The US National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines one standard drink as containing exactly 14 grams (0.6 fl oz) of pure alcohol. Common equivalents: 12 fl oz of regular beer at 5% ABV, 8–9 fl oz of malt liquor at 7% ABV, 5 fl oz of table wine at 12% ABV, 3–4 fl oz of fortified wine (sherry, port) at 17% ABV, 2–3 fl oz of cordials at 24% ABV, 1.5 fl oz of spirits (vodka, whiskey, gin, rum) at 40% ABV. Craft beers are a common miscounting trap — a 16 oz pint of IPA at 7% ABV contains approximately 1.87 standard drinks, not one. Many cocktails contain 1.5–3 standard drinks depending on recipe.
Many common medications interact dangerously with alcohol and can amplify impairment at BAC levels lower than the legal limit. Categories of concern: CNS depressants (benzodiazepines, sleep medications, opioids) — dramatically amplify sedation; even 0.04% BAC with Xanax or Ambien can produce impairment equivalent to 0.10%+ BAC alone. Antihistamines (Benadryl, many cold medicines) — increase drowsiness. Metronidazole (Flagyl) — causes severe nausea and vomiting with any alcohol. Acetaminophen (Tylenol) — combination with alcohol significantly increases liver toxicity risk. Some antibiotics and antifungals. The BAC calculator cannot account for medication interactions — anyone taking prescription or OTC medications should consult their pharmacist about alcohol interactions before drinking.
A first-offense DUI in the US carries significant consequences that vary by state but typically include: License suspension of 90 days to 1 year, fines of $1,000–$10,000 (including fees, court costs, and insurance surcharges), mandatory alcohol education classes, possible jail time of 24 hours to 6 months, ignition interlock device installation at your expense ($70–$150 installation plus $60–$80 monthly), and a criminal record. Total first-offense DUI cost in the US averages $10,000–$15,000 when all expenses are included. Aggravating factors (BAC above 0.15%, minor passengers, accident) increase penalties substantially. Commercial drivers lose their CDL for one year on a first offense — effectively ending their career. The NHTSA's message: the average cost of a rideshare home is $15–$30; the average cost of a DUI is $10,000+.