Everyday Life · Practical Life · Health & Lifestyle
Blood Alcohol Content Calculator
Estimates your blood alcohol content (BAC) based on drinks consumed, body weight, sex, and time elapsed using the Widmark formula.
Calculator
Formula
BAC is blood alcohol content in grams per 100 mL (%). A = total alcohol consumed in fluid ounces of pure alcohol (drinks × alcohol per drink). W = body weight in pounds. r = Widmark distribution constant (0.73 for males, 0.66 for females). t = hours elapsed since drinking began. The constant 5.14 converts fluid ounces of alcohol to grams per pound. The term 0.015 × t accounts for alcohol metabolism at approximately 0.015% per hour.
Source: Widmark, E.M.P. (1932). Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. Urban & Schwarzenberg. Adapted by the National Highway Traffic Safety Administration (NHTSA).
How it works
Blood alcohol content (BAC) represents the percentage of alcohol in your blood by volume. A BAC of 0.08% — the legal driving limit in the United States — means 0.08 grams of alcohol per 100 mL of blood. Even small amounts of alcohol affect reaction times, judgment, and coordination, making BAC awareness important for personal safety. Many countries set the legal driving limit lower, at 0.05% or even 0.02% for new drivers.
This calculator uses the Widmark formula, the most widely accepted mathematical model for estimating BAC. The formula is: BAC = (A × 5.14 / W × r) − (0.015 × t), where A is the total fluid ounces of pure alcohol consumed, W is body weight in pounds, r is the Widmark distribution factor (0.73 for males, 0.66 for females), and t is the number of hours since drinking began. The factor 5.14 converts fluid ounces of alcohol into grams per pound of body weight, and 0.015 represents the average rate at which the liver metabolizes alcohol per hour. Biological sex affects BAC because females typically have a higher body fat percentage and lower total body water, meaning alcohol becomes more concentrated in their bloodstream.
The Widmark formula is used by medical professionals, law enforcement agencies, and forensic toxicologists as a reliable first-order approximation of BAC. It is applied in legal proceedings, workplace alcohol testing education programs, and public health campaigns. One standard drink in the US contains approximately 0.6 fl oz (14 grams) of pure alcohol — equivalent to a 12 oz beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 80-proof spirits.
Worked example
Suppose a 170-pound male has consumed 4 standard drinks (each containing 0.6 fl oz of pure alcohol) over 2 hours.
Step 1 — Total alcohol consumed: 4 drinks × 0.6 fl oz = 2.4 fl oz of pure alcohol.
Step 2 — Apply Widmark formula (before metabolism): (2.4 × 5.14) / (170 × 0.73) = 12.336 / 124.1 = 0.0994%
Step 3 — Subtract metabolism: 0.015 × 2 hours = 0.030% metabolized.
Step 4 — Estimated BAC: 0.0994 − 0.030 = 0.069%
This individual would be below the US legal limit of 0.08%, but still noticeably impaired. To reach 0.00% BAC from the start of drinking, divide the peak BAC (0.0994%) by 0.015 = approximately 6.6 hours total. Since 2 hours have already passed, they would need roughly 4.6 more hours before fully sobering up.
Limitations & notes
This calculator provides an estimate only and should never be used to determine whether it is safe or legal to drive. Actual BAC depends on many individual factors not captured by the Widmark formula, including liver function, food intake, hydration level, medication use, tolerance, body composition, and genetics. The metabolism rate of 0.015% per hour is an average — it can range from 0.010% to 0.025% between individuals. Food significantly slows alcohol absorption, while carbonated mixers accelerate it. The Widmark r-factor also varies more broadly in practice (0.60–0.85 for males, 0.51–0.77 for females) than the fixed values used here. This tool is intended for educational awareness only — if in doubt, do not drive. Always use a designated driver, public transport, or a rideshare service.
Frequently asked questions
What is a standard drink for BAC calculation purposes?
In the United States, one standard drink contains approximately 0.6 fluid ounces (14 grams) of pure ethanol. This is equivalent to a 12 oz regular beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 80-proof distilled spirits. Different countries define standard drink sizes differently — the UK unit is 8 grams of ethanol and Australia's is 10 grams.
What BAC level is considered legally impaired for driving?
In the United States, Canada, and Australia, the legal BAC limit for driving is 0.08%. Most of Europe sets the limit at 0.05%. Some countries, including Sweden and parts of Eastern Europe, enforce limits as low as 0.02%. Commercial drivers and new/young drivers often face stricter zero-tolerance limits in many jurisdictions.
Why does biological sex affect blood alcohol content?
Females generally have a higher body fat percentage and lower total body water than males of similar weight. Since alcohol distributes through body water rather than fat tissue, it becomes more concentrated in females — leading to a higher BAC for the same amount of alcohol consumed. Females also tend to produce less alcohol dehydrogenase, the enzyme responsible for metabolizing alcohol in the stomach.
Can coffee or food sober you up faster?
No. Coffee, food, cold showers, and exercise do not speed up the liver's metabolism of alcohol. The liver processes alcohol at a fixed rate of roughly 0.015% BAC per hour regardless of what you consume or do. Food consumed before or during drinking can slow alcohol absorption into the bloodstream, but it does not reduce your BAC once alcohol is already in your system.
How accurate is the Widmark formula?
The Widmark formula is a well-validated population-level approximation widely used in forensic toxicology and legal proceedings. However, individual variation in absorption rate, metabolism, body composition, and enzyme activity means actual BAC can differ meaningfully from the estimate. Studies suggest the formula is typically accurate within ±15–20% under controlled conditions. It is most reliable when used as a general awareness guide rather than a precise measurement tool.
Last updated: 2025-01-15 · Formula verified against primary sources.