BAC Calculator (Blood Alcohol Content)

The BAC calculator above estimates your blood alcohol concentration from your sex setting, weight, drinks and the time since you started drinking. It shows your estimated BAC now, the peak if every drink were absorbed at once, and the time until the estimate reaches 0.00, with a range. The math uses Widmark's average body water constants and takes off 0.015% per hour.

How to use the BAC calculator

The blood alcohol calculator needs four inputs: the sex setting, your weight, your drinks and the hours since your first drink. Until the sex setting, weight and hours are filled in, the result panel shows a prompt, not a number.

Sex setting and body weight

The sex field, labelled "Body type used by the formula", sets Widmark's body water average, r: 0.68 for men or 0.55 for women.

Weight goes in pounds or kilograms, from 80 to 500 lb (36 to 227 kg). A BAC calculator by weight needs your real weight, because the same grams spread through more body water in a heavier body. Widmark's r scales body weight alone, so there is no height field.

Drink presets and custom drinks

Each drink row has a type, count, size and ABV, and the form opens with one 12 oz beer at 5%. Pick a preset and the row fills in its size and ABV. Change the count for repeats. The row then shows its grams and its total in US standard drinks of 14 g, the unit set out in how a US standard drink is defined.

Beer presets are regular (12 oz at 5%, 14.0 g, 1.00 drink) and light (12 oz at 4.2%, 11.8 g, 0.84 drink). Two more are a pint (16 oz at 5%, 18.7 g, 1.33 drinks) and strong craft (12 oz at 10%, 28.0 g, 2.00 drinks). Wine is 5 oz at 12% (14.0 g, 1.00 drink), and a spirits shot is 1.5 oz at 40% (14.0 g, 1.00 drink). Hard seltzer or malt liquor starts at 12 oz and 8% (22.4 g, 1.60 drinks) for you to edit.

Custom takes any size in oz or mL and any ABV from 0.5% to 95%. Add one row for each different drink.

Hours since your first drink

Enter the hours since you started drinking, from 0 to 48 in steps of 15 minutes. Every hour from the first drink takes 0.015% off the estimate. Counting from the last drink means entering fewer hours, so the result reads higher than the formula intends.

Choosing a limit line

The limit line is a reference mark drawn against your result, set to the US adult 0.08% until you change it. It is not a test, and it leaves BAC now, the peak and the time to 0.00 unchanged; it only sets the above-or-below reading. The custom option takes any value from 0.00% to 0.15%, for a country with no preset yet.

Preset group	Line values	Where the values come from
United States	0.08% adult, 0.05% Utah, 0.02% under 21, 0.04% commercial on duty	US limits by state
United Kingdom	0.08% England, Wales and Northern Ireland; 0.05% Scotland	UK drink driving limits
Australia	0.05% full licence; 0.00% learner and provisional	Australian drink driving limits

What the blood alcohol level calculator shows

The blood alcohol level calculator gives BAC now, the all-absorbed peak, the time to 0.00 with a range, and your position against the limit line. BAC shows 3 decimals, and times round up to the next 15 minutes.

Current BAC and peak BAC

BAC now is the big number: the peak minus 0.015% for each hour since your first drink, never below 0.000%. The peak is the formula's figure if every drink reached your blood at once. It is not a forecast of your highest real reading.

Beside BAC now sits an effect label. From 0.02% to 0.15% it quotes the National Highway Traffic Safety Administration (NHTSA) effect rows, which also feed the effects page that walks through every BAC level. Higher results get MedlinePlus wording.

Someone who cannot be woken, is breathing slowly or irregularly, or is vomiting while not fully awake needs an ambulance. Call 911 (US, Canada), 999 (UK), 000 (Australia), 112 or 999 (Ireland), 111 (New Zealand). The panel shows that line first once the peak or BAC now reaches 0.30%, linked to alcohol poisoning signs and BAC levels.

Time to 0.00 as a range

Time to 0.00 is BAC now divided by 0.015%, the average hourly drop for moderate drinkers. A range, "between X and Y", comes from the same BAC at 0.020% and 0.010% per hour.

That band is narrower than people really vary: A. W. Jones's 2010 review reports clearance from 0.010% to 0.035% per hour. Each end of the range marks when the estimate reaches 0.00, not a time to drive and not a test result.

Above or below your limit line

Above the line, the panel shows the time until the estimate drops below it. Below, it prints "Estimated BAC is below the selected limit" with a note that impairment starts below legal limits.

The 180 lb man in the examples below reads 0.056% now: under a 0.08% line, while his estimate stays over 0.05% for about 30 minutes. Weight, sex and hours set where a line is crossed, as how many drinks put each body weight over 0.08% makes plain.

BAC calculator examples

Type either example into this blood alcohol concentration calculator and the panel should print the outputs below. The tool divides grams of alcohol by body weight times r, then subtracts 0.015% per hour; the Widmark formula worked step by step shows each line of that math.

Field	180 lb (81.6 kg) man	135 lb (61.2 kg) woman
Input: sex setting	Male (r 0.68)	Female (r 0.55)
Input: drinks	4 x regular beer, 12 oz at 5%	2 x wine, 5 oz at 12%
Input: hours since first drink	3 hours	2 hours
Output: alcohol	56.0 g, 4.00 drinks	28.0 g, 2.00 drinks
Output: peak if all absorbed	0.101%	0.083%
Output: BAC now	0.056%	0.053%
Output: time to 0.00	about 3 h 45 min	about 3 h 45 min
Output: range at 0.020% to 0.010% an hour	3 h 0 min to 5 h 45 min	2 h 45 min to 5 h 30 min
Output: against a 0.08% line	below the selected limit	below the selected limit

Under the man's result, the panel adds one plain sentence for screen readers. It reads "Estimated BAC 0.056% now; about 3 h 45 min until 0.00 at 0.015% per hour". Set the count to 1 and the peak shows what a single drink adds at your weight. One beer's BAC rise at each body weight lists that figure across body sizes.

Both results are estimates from average constants. Food, drinking pace, body make-up and health can push a real BAC either way, and only a breath or blood test can measure it.

The r values are Widmark's averages as cited in a 2019 PLoS One study, and 0.015% per hour is the moderate-drinker average in Jones's review. The 14 g drink is the National Institute on Alcohol Abuse and Alcoholism (NIAAA) definition, and Searle's 2015 paper gives 0.789 g per mL. The panel's assumptions line names the formula, both r values, the hourly rate and full absorption.

BAC calculator for women and men

The sex setting changes only r, so at the same weight and drinks a woman's peak comes out about 24% higher (0.68 ÷ 0.55 = 1.24).

Switch the setting to male for the woman in the examples, and her 28.0 g gives a peak of 0.067% instead of 0.083%. NIAAA's fact sheet on women and alcohol puts the gap down to women having less body water pound for pound.

The setting holds one average per sex, so it cannot reflect your own build. At 160 lb, 4 drinks and 1 hour, the BAC charts for men and women side by side give 0.098% for a man and 0.125% for a woman.

How accurate is a BAC calculator?

A BAC calculator gives a rough estimate. Four studies of calculators or apps, three of them against real measurements, found sizable errors. The 2026 study's authors judged most online calculators unsuitable for assessing intoxication.

Study	What was tested	What it found
Hustad and Carey, 2005	5 equations vs breath tests of 109 drinkers	Equations read above breath on average; the best one agreed less at higher levels
Wilson and colleagues, 2016	58 drink-driving and alcohol apps, some of them calculators	Most lacked accuracy
Jama, Sekuła and Zuba, 2023	6 calculators vs breath readings in 10 drinking cases	Time to sobriety mostly ran longer than the real time; tools appeared to use Widmark's coefficient
Stragierowicz and colleagues, 2026	36 online calculators vs measured BAC in 16 fasted and fed adults	Means ran 39% to 49% above measured values

These are averages across people and tools, not a correction for your own number.

This tool runs the same Widmark arithmetic the 2023 study found in popular calculators, so it shares the limits those studies found. That is why it prints a range for time to 0.00 and no accuracy figure.

What the calculator cannot know

The tool has no food field, though food slows absorption. It also treats every drink as already absorbed and uses one average r and clearance rate for everyone.

FAQ

Conclusion

Your result changes every 15 minutes you wait, so run the calculator again with the new hours. The calculator lowers it only with time, and the tricks people try to sober up are tested one by one against studies.