BAC Calculator
Estimate blood alcohol content using the Widmark formula — for educational use only.
Educational use only. BAC estimates vary significantly by individual. Never use this tool to decide whether it is safe to drive. Always use a designated driver or rideshare service.
1 drink = 12 oz beer, 5 oz wine, or 1.5 oz spirits
Try Example
Estimated Results
BAC Levels & Effects
| BAC Level | Effects | Legal Status |
|---|---|---|
| Below 0.020% | Negligible — subtle relaxation | Under limit everywhere |
| 0.020–0.049% | Mild relaxation, reduced anxiety, slight motor impairment | Under 0.05% limit; over 0.02% (some countries) |
| 0.050–0.079% | Noticeable impairment, slower reaction time, reduced coordination | Over limit in AU, many EU countries |
| 0.080–0.149% | Clear impairment, slurred speech, poor coordination | Over legal limit in USA, UK, Canada, India |
| 0.150–0.249% | Significant impairment, nausea, potential blackout | Seriously over limit — criminal in all jurisdictions |
| 0.250%+ | Severe impairment, unconsciousness risk, potentially fatal | Medical emergency — alcohol poisoning risk |
The Widmark Formula
What Is Blood Alcohol Content (BAC)?
Blood Alcohol Content (BAC) is the concentration of alcohol in your bloodstream, expressed as a percentage. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 millilitres of blood. It is the standard measurement used by law enforcement worldwide to assess alcohol-related driving impairment.
BAC rises as you consume alcohol (because absorption into the bloodstream is faster than elimination) and falls over time as your liver metabolises the alcohol at approximately 0.015% per hour.
How the Widmark Formula Works
The Widmark formula, developed by Swedish physician Erik Widmark in 1932, remains the foundational method for estimating BAC. It calculates an estimated peak BAC based on total alcohol consumed, body weight, biological sex, and time elapsed.
The key variable r (the Widmark factor or distribution factor) accounts for the percentage of the body that is water, since alcohol distributes through body water. Men average 0.73 because they have proportionally more muscle (which holds water) and less body fat. Women average 0.66 because they typically have a higher proportion of body fat, which does not absorb alcohol.
Factors That Affect BAC
- Body weight: Heavier people have more body water for alcohol to distribute through, resulting in lower BAC.
- Biological sex: Women reach higher BAC than men of the same weight due to body composition and enzyme differences.
- Food consumption: Eating before or during drinking slows alcohol absorption into the bloodstream, delaying peak BAC — but does not speed up elimination.
- Alcohol strength: Drinks with higher ABV contain more pure alcohol. A double spirit has twice the alcohol of a single.
- Rate of consumption: Drinking faster raises BAC faster because absorption outpaces elimination.
- Medication and genetics: Some medications interact with alcohol. Genetic variations in alcohol dehydrogenase enzymes affect elimination rates.
Legal BAC Limits by Country
| Country | Legal Limit (Driving) | Notes |
|---|---|---|
| USA | 0.08% | 0.04% for commercial drivers; 0.00–0.02% for under-21 (varies by state) |
| UK (England/Wales) | 0.08% | Scotland: 0.05% |
| Australia | 0.05% | 0.00% for learners and probationary drivers |
| Germany / France | 0.05% | 0.00% for new drivers in Germany |
| India | 0.03% | One of the lowest limits in the world |
| UAE / Saudi Arabia | 0.00% | Zero tolerance — any alcohol is illegal |
How Long Does Alcohol Stay in Your System?
The body eliminates alcohol at a fairly constant rate of approximately 0.015% BAC per hour, regardless of coffee, cold showers, or exercise (these are myths). If your estimated BAC is 0.09%, it will take about 6 hours to reach 0.00%. Urine and breath tests can detect alcohol for 12–24 hours after consumption; hair tests can detect it for months.
The "One Drink Per Hour" Rule — Why It's an Oversimplification
The common rule of thumb that "one drink per hour" keeps you sober is unreliable. It approximates the average elimination rate for a 160 lb (73 kg) male. For a 120 lb (54 kg) woman, one drink per hour would result in gradual BAC accumulation. Body weight, sex, food intake, and drink strength all affect the actual rate. Use the calculator above rather than relying on rules of thumb.
Frequently Asked Questions
BAC (Blood Alcohol Content) is the concentration of alcohol in your bloodstream, expressed as a percentage by volume. A BAC of 0.08% means 0.08 g of alcohol per 100 mL of blood. It is the standard measure for assessing impairment level and is used in DUI laws worldwide. BAC rises as alcohol is absorbed and falls as the liver metabolises it.
The Widmark formula is used: BAC = (A × 5.14) / (W × r) − 0.015 × H, where A = total alcohol in ounces (drinks × 0.6), W = body weight in lbs, r = 0.73 (male) / 0.66 (female), and H = hours since first drink. The 0.015 accounts for the average alcohol elimination rate of roughly 0.015% BAC per hour.
Limits vary by country: USA 0.08%, UK 0.08% (Scotland 0.05%), Australia 0.05%, most EU countries 0.05%, India 0.03%. Some countries (UAE, Saudi Arabia, Hungary) have zero-tolerance laws. Commercial drivers and new/young drivers typically face lower limits. Always check your local jurisdiction.
The body eliminates alcohol at approximately 0.015% BAC per hour. Divide your estimated BAC by 0.015 to get the hours needed to reach zero. A BAC of 0.09% takes about 6 hours. Cold showers, coffee, exercise, and food do NOT speed up this process — only time reduces BAC. These myths persist but have no basis in physiology.
Food eaten before or during drinking slows alcohol absorption into the bloodstream — it acts as a buffer that delays peak BAC and reduces how high BAC gets. However, food does not speed up alcohol elimination. Once alcohol is absorbed, the liver metabolises it at the same rate regardless. If you ate a full meal before drinking, your actual BAC may be noticeably lower than the calculator estimates.
Women generally reach higher BAC than men of the same weight with the same amount of alcohol for two reasons: (1) women have proportionally more body fat and less body water — since alcohol distributes in water, there is less water to dilute it; (2) women typically produce lower levels of alcohol dehydrogenase (ADH), an enzyme that starts breaking down alcohol in the stomach before it reaches the bloodstream. The Widmark r-factor of 0.73 (male) vs 0.66 (female) accounts for this difference.
In the United States, one standard drink contains 14 grams (0.6 fl oz) of pure ethanol. This equals: 12 oz regular beer at 5% ABV, 5 oz wine at 12% ABV, or 1.5 oz distilled spirits at 40% ABV. Many countries use different definitions — the UK defines 8g, Australia 10g. Craft beers (7–10% ABV) or large pours can contain 1.5–2 standard drinks per serving.
No — absolutely not. This calculator provides a rough educational estimate only. Actual BAC varies significantly based on individual metabolism, food intake, medication interactions, hydration, and other factors not captured by the formula. Even a small amount of alcohol impairs judgment and reaction time below the legal limit. If you have consumed alcohol, use a designated driver, taxi, or rideshare service — always.