BAC Calculator
Enter your weight, sex, drinks and hours since the first drink to see a rough estimate of blood alcohol concentration. It is an educational estimate, not a measurement, and never a signal that it is safe to drive.
Last updated November 4, 2026
Rough estimate only. Do not drive after drinking. This is not a breathalyzer, not legal evidence and not proof you are fit to drive. You can be impaired below any legal limit, and the estimate can be wrong.
Sets the Widmark ratio
Result
Rough estimate only: about 0.082% BAC (range 0.060% to 0.109%)
| Measure | Value |
|---|---|
| Alcohol consumed | 42 g (3 US standard drinks) |
| Estimate (default assumptions) | 0.082% |
| Lower end of range | 0.060% |
| Upper end of range | 0.109% |
| Time until near 0 (do not rely on it) | 5.5 h (3 h to 10.9 h) |
Do not drive after drinking. This is not a breathalyzer, not legal evidence and not proof you are fit to drive. You can be impaired below any legal limit, and the estimate can be wrong. Estimated time until near 0: about 5.5 h (range 3 h to 10.9 h). Do not rely on it. Food, medication, health, genetics, tolerance, drink strength and drinking pace change real BAC.
Show the work
Formula: Widmark: BAC % = alcohol (g) ÷ (body weight (g) × r) × 100 − β × hours, not below 0. r = 0.68 (male) or 0.55 (female); β = 0.015 % per hour by default (a convention; published average about 0.018).
- You entered 150 lb (68 kg = 68,039 g), female, 3 drinks, 2 h.
- Alcohol = 3 × 14 g = 42 g.
- Peak = 42 ÷ (68,039 × 0.55) × 100 = 0.112%.
- After 2 h: 0.112% − 0.015 × 2 = 0.082% (not below 0).
- Range: lower, r 0.62 and β 0.02: 0.060%; upper, r 0.48 and β 0.01: 0.109%. r varies by ±0.07 here as an illustration.
- Time until near 0 = peak ÷ β − hours elapsed = 0.112% ÷ 0.015 − 2 = 5.5 h. Do not rely on it.
Result: Rough estimate only: about 0.082% BAC (range 0.060% to 0.109%)
How the BAC estimate works
BAC % = alcohol (g) ÷ (body weight (g) × r) × 100 − β × hours
The Widmark formula spreads the alcohol you drank through your body water. Alcohol grams come from your drinks: a US standard drink holds 14 g of pure alcohol, and for other drinks the calculator uses volume × alcohol by volume × 0.789 g/ml (the density of ethanol).
The ratio r is Widmark’s 1932 average, 0.68 for men and 0.55 for women, because the average body holds less water per kilogram in women; people differ widely around those averages. The elimination rate β is set to 0.015% per hour, a commonly used convention that is below the published average of about 0.018% per hour (reported range 0.009 to 0.035). The result never drops below 0.
Because r and β vary, the page shows a range: the lower end uses a higher r and faster elimination (β 0.020), and the upper end uses a lower r and slower elimination (β 0.010). Real values can fall outside it: the published spread of r and β is wider than this range.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Also useful alongside this calculator: BMI Calculator, Date Calculator and Ideal Weight Calculator.
This is an estimate, not medical advice
This is a rough educational estimate. It is not a breathalyzer, not a blood test, not legal evidence and not proof that you are fit to drive, and it does not replace advice from a doctor or other qualified health professional. This page has not been reviewed by a medical professional. Do not drive after drinking.
Do not drive after drinking
This calculator cannot tell you whether you are safe to drive, and it never will. It is not a breathalyzer, its output is not legal evidence, and you can be impaired at levels below any legal limit. Legal limits depend on the jurisdiction and the type of driver. Every US state sets 0.08% except Utah, which set 0.05% for drivers 21 and over in noncommercial vehicles from December 30, 2018. Federal rules treat 0.04% or more as disqualifying for commercial truck and bus drivers, and states set limits of 0.02% or lower for drivers under 21. No level of alcohol is a safe amount to drive on. See the source notes for what we could not re-verify.
If you have been drinking, arrange another way home. The time shown as estimated time until near 0 is only the model’s guess. Do not rely on it.
What the estimate leaves out
The formula assumes every drink is absorbed at once and ignores most of what matters in real life: food in your stomach, how fast you drink, medications, health conditions, genetics, tolerance, and the true strength and size of your drinks. Pour sizes and alcohol content vary widely, so counting standard drinks from a bar or home pour is often wrong. Two people with the same numbers can have quite different results.
Body weight, not fitness, drives the formula, so it says nothing about body fat or hydration.
Sources
Official and primary sources for the statements on this page. Their authors have not reviewed or endorsed this page.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA), What Is A Standard Drink? (web page, checked November 4, 2026). States that a US standard drink contains about 14 grams (0.6 fluid ounces) of pure alcohol, as in a 12-ounce regular beer at 5% alcohol by volume, a 5-ounce glass of wine at 12% or 1.5 ounces of 80-proof spirits at 40%
- National Highway Traffic Safety Administration (NHTSA), Drunk Driving (web page; the page itself returned HTTP 403 to our automated check on November 4, 2026). NHTSA text seen in search results, not on the page itself: every state has a 0.08 g/dL illegal per se limit except Utah, which enacted 0.05 g/dL effective December 30, 2018, and all states have limits of 0.02 g/dL or lower for drivers under 21
- Utah Highway Safety Office, 0.05 BAC Law (web page, checked November 4, 2026). States that the per se limit was lowered from 0.08 to 0.05 g/dL effective December 30, 2018 (House Bill 155); the page does not say which drivers it covers
- Electronic Code of Federal Regulations, 49 CFR 382.201 Alcohol concentration (search result summary, November 4, 2026). A commercial driver may not perform safety-sensitive functions with an alcohol concentration of 0.04 or more
- Posey D, Mozayani A. The estimation of blood alcohol concentration: Widmark revisited. Forensic Sci Med Pathol 2007;3(1):33-39 (bibliographic record confirmed; the paper itself is paywalled and was not opened). Reviews Widmark-type models for estimating blood alcohol concentration. The r and elimination figures below were read from summaries of this work, not from the paper
Verified from secondary summaries only: Widmark’s 1932 r values of 0.68 for men and 0.55 for women (about ±0.17 and ±0.11; NIST presentation slides call them outdated) and an elimination rate averaging about 0.018% per hour with a reported range of 0.009 to 0.035. Our default of 0.015% per hour is a commonly used convention below that average, and the ±0.07 spread on r and the 0.010 to 0.020 range on β are illustrations narrower than the published variation, so the range shown can miss real values.
Not verified against a source: that impairment can occur below 0.08% (stated as a caution, not a measured threshold), and the exact scope of Utah’s 0.05% limit (the page we opened does not say who it covers; other reports say drivers 21 and over in noncommercial vehicles). Legal limits differ by place and by driver, so check your own jurisdiction. No amount of alcohol is presented as safe for driving.
How to use the BAC Calculator
- Choose units, sex and enter your weight.
- Enter the number of drinks, using US standard drinks or a custom size and alcohol percentage.
- Enter the hours since your first drink.
- Read the estimated range, keep the warning in mind, then use Copy, Print or Share if you need to.
Worked example
A man weighing 80 kg has 4 US standard drinks (56 g of alcohol), and 2 hours have passed. The peak is 56 ÷ (80,000 × 0.68) × 100 = 0.103%. After 2 hours at 0.015% per hour the estimate is 0.103 − 0.030 = 0.073%, and the range is 0.053% to 0.095%.
| Assumption | Estimate after 2 hours |
|---|---|
| Lower end (r 0.75, β 0.020) | 0.053% |
| Default (r 0.68, β 0.015) | 0.073% |
| Upper end (r 0.61, β 0.010) | 0.095% |
Frequently asked questions
How many drinks is 0.08% BAC?
It depends on your weight, sex, pace and food, so no drink count is reliable; use the range as a rough guide only and never as a driving limit.
How long does it take to sober up?
The model assumes the body clears 0.015% per hour, but published rates range from about 0.009 to 0.035% per hour, and coffee, showers or water do not speed it up.
Is this calculator accurate enough to decide if I can drive?
No. It is a rough estimate with wide error, it is not a breathalyzer, and impairment can begin well below legal limits, so do not drive after drinking.
Why is the result different for men and women?
The Widmark ratio is lower for women on average (0.55 versus 0.68), so the same alcohol gives a higher concentration at the same weight.
Are my numbers stored or sent anywhere?
No. The calculation runs in your browser and nothing you enter is saved or uploaded.