BAC Estimate Calculator.

Formula or algorithm and variables.

Equation, units, and population

estimated BAC (%) = (alcohol grams ÷ (weight grams × r)) × 100 − 0.015 × hours. One US standard drink is modeled as 14 grams of pure alcohol. r is a population-average distribution factor, not a measurement of an individual. This page names the equation rather than presenting an unexplained score. Check that every value uses the displayed unit and that you belong to the population for which the method is described. The calculation retains full precision internally and rounds only the visible result. A reproducible estimate should let another reader use the same inputs and reach the same arithmetic answer, while still recognizing that mathematical reproducibility does not prove medical suitability.

Worked example

For an 80 kg person, two modeled standard drinks contain 28 g alcohol. With r = 0.68, the starting estimate is about 0.051%; subtracting two hours at 0.015 percentage points per hour gives about 0.021%. Work through the example by writing the equation, substituting each labeled input, and preserving units at every step. The example demonstrates arithmetic only; it is not a recommended body measurement, intake, exercise level, laboratory value, or date. Replace every example input with the values from the situation being considered, and retain those inputs with any result you copy. Small differences can arise from rounding, equation versions, atomic-weight conventions, or date boundaries.

Interpreting the estimate

The result is a rough population-model estimate in percent g/dL. It is not a clearance time, legal opinion, impairment test, or assurance of safe driving. Health calculations compress complex biology into a few inputs, so the result should be read as context rather than a verdict. Do not compare two people as though the higher or lower number is automatically better. Look for changes over time only when the method, units, and conditions are consistent. If a result conflicts with symptoms, a laboratory report, a clinician’s instructions, or a validated measurement, rely on the appropriate professional evidence rather than this calculator.

Validation and edge cases

Weight must be 30–300 kg, drinks 0–30, elapsed time 0–48 hours, and the selected distribution factor must be supported. Negative estimates are displayed as zero. Blank, malformed, nonfinite, and out-of-domain inputs fail explicitly without producing NaN or infinity. The bounds prevent obviously implausible values from being mistaken for meaningful answers, but passing a range check does not make an input medically correct. Recheck dates, decimal separators, unit conversions, coefficient choices, and whether a laboratory value uses the expected assay and unit. Contact a qualified professional when a result could affect treatment, medication, pregnancy care, nutrition therapy, or exercise safety.

Limitations and responsible use

Food, drink size, drinking speed, medicines, health, metabolism, biological variation, and measurement timing can materially change BAC. Only a validated breath or blood test measures BAC. Never use this estimate to decide whether to drive. Any alcohol can impair driving, legal limits vary, and an individual BAC can be higher than this estimate. FigureNest processes these inputs locally in the browser and does not send them to a calculation service. The page does not create a medical record, assess symptoms, or know personal history. Avoid using estimates to shame a body, pursue unsafe restriction, delay care, determine legal fitness, or replace contraception. Authoritative source links are provided so readers can check the equation version and current guidance before making a consequential decision.

Check assumptions and sources.

Food, drink size, drinking speed, medicines, health, metabolism, biological variation, and measurement timing can materially change BAC. Only a validated breath or blood test measures BAC.

CDC Impaired Driving

NHTSA — The ABCs of BAC