How to use the BAC calculator
- Add your details. Enter your body weight and choose the sex option that fits best, or “Not sure”. Both stay in your browser.
- Add your drinks. Tap a drink type. Use Several at once to count drinks and say when you drank — recently, last night, or times you choose — or One at a time to give each drink its own time. Check the strength (ABV) on the label: the prefilled values are typical figures.
- Read the estimate as a range. The large number is the central estimate. The range shows how far it moves for people who absorb and process alcohol differently.
Logging the night before works the same way: choose Last night and correct the start and finish times, or give single drinks their own time and use “I don’t remember exactly” when you only know roughly when a drink happened. See alcohol the morning after.
What is BAC?
Blood alcohol concentration (BAC), also called blood alcohol content, is the amount of alcohol in a given volume of blood. In the United States it is written as a percentage that means grams of alcohol per 100 mL of blood, so 0.08 % is 0.08 g per 100 mL. Other countries write the same quantity in other units.
| Unit | Meaning | Example |
|---|---|---|
| % BAC | grams per 100 mL of blood (g/dL) | 0.08 % |
| mg/100 mL | milligrams per 100 mL of blood | 80 mg/100 mL |
| g/L | grams per litre of blood | 0.8 g/L |
| ‰ by mass | grams per kilogram of blood | 0.76 g/kg |
The percent sign in “% BAC” is a convention for grams per 100 mL. It is not a percentage by volume, and it is not the same as the per-mille by mass used in some European countries. You can switch units in Settings; the calculation does not change.
When will I be sober?
No calculator can tell you when you have sobered up. This one estimates when your blood alcohol returns to near zero if you drink nothing more, and it shows that time as a window because people eliminate alcohol at different rates: forensic guidance uses a range of 0.010 to 0.025 g/dL per hour, with about 0.015 g/dL per hour as an average for moderate drinkers.
Sources: AAFS Standards Board, Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology; Jones AW, Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework.
Near zero is also not the same as recovered. Hangover symptoms peak when blood alcohol returns to about zero, and attention, decision-making and coordination can still be impaired. Coffee, a cold shower or sleep do not make the body process alcohol faster; only time does.
Sources: National Institute on Alcohol Abuse and Alcoholism, Hangovers; National Institute on Alcohol Abuse and Alcoholism, The Truth About Holiday Spirits.
Why you can’t use it to decide about driving
Driving ability is affected at blood alcohol levels well below common legal limits, and you cannot reliably judge your own level. The table summarises what the US road-safety agency NHTSA lists as predictable effects on driving.
| BAC (g/dL) | Predictable effects on driving |
|---|---|
| 0.02 | Weaker visual tracking of moving objects; harder to do two things at once. |
| 0.05 | Reduced coordination, difficulty steering, slower response to emergencies. |
| 0.08 | Poorer concentration, speed control and perception; short-term memory loss. |
| 0.10 | Reduced ability to stay in lane and brake appropriately. |
| 0.15 | Substantial impairment in vehicle control and attention to driving. |
Sources: National Highway Traffic Safety Administration, Drunk Driving.
If you have been drinking, don’t drive. An estimate from body weight and a drink list can be wrong by a wide margin for you personally, legal limits differ between countries, and impairment starts before any limit. The UK Department for Transport puts it plainly: you cannot reliably calculate how much you can drink and stay under the limit.
Sources: UK Department for Transport, THINK! Drink driving.
How accurate is a BAC calculator?
A BAC calculator turns a known amount of alcohol into an estimate of concentration using population averages. Three kinds of numbers are involved, and they deserve different levels of trust.
- A calculation you can check. Grams of alcohol in a drink are volume in mL × (ABV ÷ 100) × 0.789 g/mL. If the volume and ABV you entered are right, this figure is right.
- Model assumptions. How much of your body the alcohol spreads through, how fast it is absorbed and how fast it is eliminated are taken from published ranges, not measured on you.
- Individual variation. Food, medicines, body composition, genetics, liver health and drinking history all shift the real curve. The model asks about none of them and applies no correction factors for them.
The forensic standard this calculator follows states that a person’s exact volume of distribution and elimination rate at a given time cannot be known, and that results should be given as a range rather than a single value. That is why every result here comes with a range. The range shows how the result changes across those published parameter ranges (a sensitivity range). It is not a confidence interval and not a guaranteed limit.
Sources: AAFS Standards Board, Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology; John Searle, Alcohol calculations and their uncertainty.
The full method, parameters and worked examples are on how the calculator works.
Common questions
How is blood alcohol content calculated?
The calculator uses a Widmark-type model: the grams of alcohol absorbed so far are divided by body weight times a distribution volume (0.71 L/kg for the male set, 0.58 L/kg for the female set), and a steady elimination of about 0.15 g/L per hour is subtracted for the body as a whole. Each drink is absorbed gradually rather than appearing at once.
Sources: AAFS Standards Board, Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology; Maskell PD, Population ranges for the volume of distribution (Vd) of alcohol for use in forensic alcohol calculations.
Why can my BAC keep rising after my last drink?
Alcohol in the stomach and intestine keeps entering the bloodstream after you stop drinking. It can take up to about two hours after the last drink before absorption is complete, so the highest level often comes after the last sip.
Sources: National Institute on Alcohol Abuse and Alcoholism, Understanding the Dangers of Alcohol Overdose; AAFS Standards Board, Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology.
Does food, water or coffee lower BAC?
Food slows absorption and can lower the peak, but nothing you eat or drink afterwards speeds up elimination. Coffee can make you feel more awake without changing your blood alcohol or your coordination. The calculator does not model food; its range covers slow and fast absorption instead.
Sources: National Institute on Alcohol Abuse and Alcoholism, The Truth About Holiday Spirits; National Institute on Alcohol Abuse and Alcoholism, The Basics: Defining How Much Alcohol is Too Much.
How many drinks is a BAC of 0.08?
There is no fixed number, because it depends on body size, sex, drink strength and time. As a rough reference, NIAAA describes binge drinking as a pattern that brings BAC to 0.08 % or more, which typically happens after 4 or more US standard drinks for a woman or 5 or more for a man within about two hours. Use the calculator with your own figures instead of a rule of thumb, and remember that real drinks are often larger and stronger than a standard drink. The standard drink calculator shows how much alcohol a drink contains.
Sources: National Institute on Alcohol Abuse and Alcoholism, The Basics: Defining How Much Alcohol is Too Much; National Institute on Alcohol Abuse and Alcoholism, What Is A Standard Drink?.
Why is the range so wide?
Because the differences between people are large. Elimination alone ranges from 0.010 to 0.025 g/dL per hour in the guidance used here, a 2.5-fold spread, and body-water share varies as well. A narrow range would look more convincing and be less honest.
Do you send my drink log to a server?
No. Your entries stay in this browser: the calculation runs on your device and nothing you enter is transmitted.
Where is my log kept, and for how long?
In this browser tab, until you close it. If you switch on “Remember on this device”, it is kept in this browser until you clear it. “Clear my data” in the settings removes it at any time. Details are in the privacy note.
Sources
- AAFS Standards Board. Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology. ANSI/ASB Best Practice Recommendation 122, First Edition, 2024. aafs.org (checked 6 November 2026)Formula (dose ÷ (Vd × body mass)); volume-of-distribution ranges by sex; elimination range 0.010–0.025 g/dL per hour; ranges instead of single values; linear elimination unreliable below 0.020 g/dL; up to 2 hours to finish absorbing; ethanol density 0.789 g/mL.
- John Searle. Alcohol calculations and their uncertainty. Medicine, Science and the Law 2015;55(1):58–64 (with erratum 55(2):145). pmc.ncbi.nlm.nih.gov (checked 6 November 2026)Widmark formula and symbols; worked examples used as test references; the uncertainty of a calculation is not a fixed percentage and grows as the level falls; an error range must be quoted.
- Maskell PD, Heymsfield SB, Shapses S, Limoges JF. Population ranges for the volume of distribution (Vd) of alcohol for use in forensic alcohol calculations. Journal of Forensic Sciences 2023;68(5):1843–1845 (letter). eprints.gla.ac.uk (checked 6 November 2026)Median volume of distribution 0.71 L/kg in men and 0.58 L/kg in women.
- Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Science International 2010;200(1–3):1–20. pubmed.ncbi.nlm.nih.gov (checked 6 November 2026, abstract only)15 mg/100 mL per hour as a good average elimination rate for moderate drinkers; physiological range 10–35; zero-order kinetics adequate above 20 mg/100 mL.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). The Basics: Defining How Much Alcohol is Too Much. niaaa.nih.gov (checked 6 November 2026)How alcohol is absorbed, distributed and metabolised; effect of an empty stomach; body-water difference between women and men; drinks often contain more alcohol than people think.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). What Is A Standard Drink?. niaaa.nih.gov (checked 6 November 2026)US standard drink: about 14 g (0.6 US fl oz) of pure alcohol; example servings; strength varies within and across drink types.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). The Truth About Holiday Spirits. niaaa.nih.gov (checked 6 November 2026)Alcohol keeps entering the bloodstream after the last drink; coffee does not sober you up; food slows absorption.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). Hangovers. niaaa.nih.gov (checked 6 November 2026)Hangover symptoms peak when blood alcohol returns to about zero and can last 24 hours or longer; attention, decision-making and coordination can be impaired; no cure other than time.
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). Understanding the Dangers of Alcohol Overdose. niaaa.nih.gov (checked 6 November 2026)Critical signs of alcohol overdose; do not wait for all symptoms; blood alcohol can keep rising after drinking stops; what to do while waiting for help.
- National Highway Traffic Safety Administration (NHTSA). Drunk Driving. nhtsa.gov (checked 6 November 2026)Effects of blood alcohol levels on driving from 0.02 g/dL upwards; even small amounts affect driving; it is very difficult to assess your own level or impairment.
- NHS (UK). Alcohol poisoning. nhs.uk (checked 6 November 2026)Symptoms of alcohol poisoning and what to do and not do while waiting for help.
- UK Department for Transport. THINK! Drink driving. think.gov.uk (checked 6 November 2026)You cannot reliably calculate how much you can drink and stay under a legal limit; feeling fine does not mean your driving is unaffected.