Blood Alcohol Concentration (BAC) Calculator
Estimate a theoretical BAC from pure alcohol, body mass, a distribution factor and elapsed time. Never use the result to decide whether to drive, work, swim or perform any safety-critical activity.
Enter an alcohol scenario
Educational estimate only. Never use a calculated BAC to decide whether to drive or to assess a medical emergency.
What this model does and does not measure
The calculator uses a simplified Widmark-style relationship. It divides entered grams of alcohol by an assumed distribution volume based on body mass, then subtracts a constant hourly elimination amount. The output is expressed in grams per decilitre, numerically the same as a BAC percentage. It is a theoretical estimate from assumptions, not a measurement of alcohol in your blood or breath.
Real absorption and elimination are not linear clocks. Food, drink strength, pace, medicines, liver health, body composition, recent drinking, illness and individual biology can change the curve. Alcohol may continue entering the bloodstream after the last drink, so subtracting elapsed time from an estimated peak can understate BAC during absorption. No online input set can remove that uncertainty.
Count grams, not glasses
A glass, can, bottle or mixed drink is not a fixed dose. Pure alcohol depends on beverage volume and alcohol by volume. A large wine pour, strong craft beer or double spirit can contain several times the alcohol in a smaller serving. The drink-count field is meaningful only when the grams-per-drink field reflects what was actually consumed.
To estimate grams, multiply millilitres of beverage by its alcohol fraction and by ethanol density, approximately 0.789 grams per millilitre. For example, 150 mL at 12% contains about 14.2 grams: 150 times 0.12 times 0.789. Labels, pours and cocktail recipes are often uncertain, which should widen caution rather than justify a precise conclusion.
Distribution factor is an assumption
The distribution factor approximates how alcohol spreads through body water. Traditional tables often provide sex-based averages, but any single value hides variation in body composition and physiology. This tool exposes the factor so the assumption is visible. It must not be treated as a personal measurement or adjusted until the answer looks acceptable.
A lower factor produces a higher estimated concentration because the same alcohol is distributed through a smaller modelled volume. Comparing 0.55 and 0.68 demonstrates sensitivity, but neither result establishes an individual’s BAC. For medical, forensic or legal purposes, properly collected and calibrated testing is required, with interpretation by qualified professionals.
Elapsed time and elimination
The default elimination assumption of 0.015 g/dL per hour is a rough planning value found in many educational models. Individuals vary, and the body does not reliably speed elimination with coffee, cold showers, vomiting, exercise, sleep or food after drinking. Those actions may change alertness or comfort without removing alcohol at a safe, predictable rate.
The modelled time-to-zero divides the remaining estimate by the entered elimination rate. It is especially unsafe as a countdown because the estimated starting value can be wrong and absorption may not be complete. If transport or work safety matters, choose a conservative alternative that does not depend on the countdown: a sober driver, public transport, accommodation or postponement.
Why no legal-limit verdict appears
A calculator should not label a person legal to drive. Laws can distinguish driver categories and may be amended, while enforcement relies on prescribed evidence rather than an online model. More importantly, crash risk begins at low BAC levels. The World Health Organization reports increasing risk from low concentrations and a marked increase around 0.04 g/dL.
Impairment involves attention, reaction, coordination and judgement before a person necessarily feels drunk. Self-assessment is unreliable because alcohol itself affects judgement. The result panel therefore gives one safety message regardless of the number: do not drive or perform safety-critical tasks after drinking. A low displayed estimate is not a safety certificate.
Worked sensitivity example
Suppose three servings are entered at 12 grams each, body mass is 75 kg, factor is 0.68 and two hours have elapsed. The model first estimates concentration from 36 grams divided by the distribution term, then subtracts two hourly elimination amounts. Changing only the grams per serving from 12 to 20 substantially increases the result, showing why an accurate pour matters.
Now lower the distribution factor or shorten elapsed time. Each change moves the estimate in a predictable direction, but the spread between scenarios is not a confidence interval. It merely shows how dependent the answer is on unverified assumptions. When the consequence is injury, arrest or death, sensitivity should lead to more caution, not selection of the most favourable scenario.
When urgent help may be needed
Severe alcohol poisoning is a medical emergency. Confusion, inability to stay awake, repeated vomiting, seizures, slow or irregular breathing, pale or blue-tinged skin, very low body temperature or unconsciousness require urgent assistance. Do not leave an unconscious person alone, do not assume they can sleep it off, and do not rely on this calculator to grade severity.
Call local emergency services and follow their instructions. Place an unconscious breathing person in a recovery position if you know how, monitor breathing and protect them from choking. Mixing alcohol with sedatives, opioids or other drugs can increase danger. A numerical BAC estimate must never delay emergency care or replace a clinical assessment.
Responsible use of the output
Use the result only to learn how drink strength, body mass, time and modelling assumptions interact. It may support education or a retrospective classroom exercise where nobody’s immediate safety depends on it. Record all inputs and state plainly that the value was estimated, especially if comparing scenarios.
Do not use the calculator to plan how much to drink before driving, to challenge a breath test, to supervise another person’s health, or to decide fitness for work. The safest BAC for driving is zero achieved by not drinking before driving, with transport arranged in advance. If drinking is causing concern, seek help from a qualified health service.
Questions that affect this result
Can coffee or a cold shower lower BAC quickly?
No reliable shortcut removes alcohol from the body. These may change how awake someone feels without making driving safe.
Why can my real BAC differ from the estimate?
Drink strength, absorption, food, body composition, health and elimination vary. The distribution and elimination values are population assumptions, not measurements.
Does a result below a legal threshold mean I may drive?
No. This calculator gives no legal or safety clearance. Use a sober driver or another safe transport option after drinking.
What if the calculator shows zero?
A modelled zero can still be wrong because inputs and timing are uncertain. It is not a breath test and must not be used to authorise driving.
Is the time-to-zero a waiting-time guarantee?
No. It is arithmetic based on the entered elimination rate and estimated starting BAC. Actual absorption and clearance can differ materially.