Blood Alcohol Calculator
Estimate blood alcohol concentration by the Widmark equation — and understand why no estimate can tell you it is safe to drive.
Blood Alcohol Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Widmark is a 1932 population approximation with wide individual error.
- Assumes complete absorption; a recent drink means the true level may still be rising.
- Elimination rates vary roughly twofold between individuals.
In short: Four standard drinks for a 75 kg man, three hours ago, estimates at 0.065% — below the 0.08% limit but above the 0.05% limit used across much of the world. Widmark carries wide individual error and cannot establish fitness to drive.
Formula
Widmark, 1932. A population approximation with wide individual error.
Worked Example
- Total the alcohol. 4 standard drinks × 14 g = 56 g of ethanol.
- Compute body water. 75,000 g × 0.68 = 51,000 g of body water.
- Divide and scale. 56 ÷ 51,000 × 100 = 0.1098% peak.
- Subtract elimination. 0.015%/hour × 3 hours = 0.045%, giving 0.065%.
- Read both limits. Below 0.08% but above 0.05% — legal in one country, illegal in another.
This worked example lands deliberately between the two limits in common use, because that is where a single-verdict calculator does the most damage. At an estimated 0.065% the same person is under the limit in most of the United States and over it across most of Europe, in Australia and in Utah. Two further points make the number less reassuring than it looks. The margin below 0.08% is roughly 0.015 percentage points, which is comfortably inside Widmark's error — individual elimination rates alone range from about 0.010 to 0.020% per hour. And if the last drink was recent, absorption may still be pushing the true figure upward while this arithmetic assumes it is falling. Impairment of judgement and reaction time is measurable well below every legal threshold anyway.
Strengths & Limits Of This Model
Where this engine is strong
- Evaluates against both the 0.08% and 0.05% limits rather than one.
- Exposes the body water constant as the dominant term.
- Carries an explicit alcohol poisoning stop-rule.
Where it stops
- Cannot establish fitness to drive and has no legal standing.
- Cannot model absorption still in progress.
Practical Use Cases
Understanding how long alcohol lingers
Elimination is roughly 0.015% per hour and nothing accelerates it.
Seeing why the same drinks affect people differently
Alcohol distributes into body water, so body composition drives the result.
Understanding the two common legal limits
0.08% and 0.05% are both in force in different places, and this figure can straddle them.
Planning the morning after
A high evening peak can still leave measurable alcohol at breakfast.
Methodology & Editorial Standards
Blood alcohol concentration is estimated using the Widmark equation, which divides the mass of ethanol consumed by the product of body mass and a distribution constant representing the body water fraction, then subtracts elimination at a nominal rate of 0.015 percent per hour. The distribution constant is the dominant term and is offered as a selectable parameter rather than inferred from sex alone, because body composition rather than sex per se determines how alcohol distributes. The engine evaluates the result against both the 0.08 percent limit common in the United States and the 0.05 percent limit in force across much of Europe and Australia, because a verdict against a single jurisdiction is misleading wherever a result falls between them, as the worked example does. The engine states the error structure explicitly: Widmark dates from 1932, real elimination rates range roughly from 0.010 to 0.020 percent per hour, and absorption may still be raising true concentration for some time after the last drink, so an estimate can understate as easily as overstate. It states that no intervention accelerates elimination, and it carries an explicit alcohol poisoning stop-rule. No output constitutes evidence of fitness to drive. This calculator is an educational estimate and is not medical advice, diagnosis or treatment. It cannot assess your clinical condition, and no result here should be used to start, stop or change any medication or treatment. Discuss results with a qualified clinician who has access to your full history. The engine implements the standard published formula for this calculation. Inputs are validated for domain and sign before evaluation, and any undefined case returns an em-dash rather than a spurious value.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Blood Alcohol Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How is BAC calculated?
Widmark: grams of alcohol divided by body mass times a body water constant, less 0.015% per hour elapsed.
What is a standard drink?
About 14 g of pure alcohol in the US, 10 g in the UK and Australia. Enter the figure that applies.
How fast does alcohol leave the body?
Roughly 0.015% per hour, though individual rates range from about 0.010 to 0.020%.
Can I speed up sobering?
No. Coffee, showers, food and exercise change how awake you feel, not your blood alcohol.
Why does the same amount affect people differently?
Alcohol distributes into body water, so body composition rather than weight alone drives the level.
What is the legal limit?
0.08% in most of the US, 0.05% across much of Europe and Australia, and zero for many new drivers.
Is this accurate enough to drive on?
No. The error is wide enough to cross a legal limit, and impairment begins below every limit.
Can my BAC still be rising?
Yes. Absorption continues for 30 to 90 minutes or longer after the last drink, especially without food.
Will I be sober by morning?
Not necessarily. A high evening peak can leave measurable alcohol at breakfast.
Does food prevent intoxication?
It slows absorption and lowers the peak, but the same total alcohol is still absorbed.
What is the r value?
The body water fraction — roughly 0.68 in men and 0.55 in women, varying with body composition.
At what level is alcohol dangerous?
Above roughly 0.30% risks coma and respiratory depression. Poisoning is an emergency at any level with symptoms.
What are the signs of alcohol poisoning?
Confusion, vomiting while drowsy, seizures, slow or irregular breathing, cold or bluish skin, unrousable.
Should someone sleep it off?
Never unattended and never face-up. Blood alcohol can keep rising after the last drink.
Does medication affect BAC?
Many medications interact with alcohol, altering both its effect and its clearance. Check with a pharmacist.
Is this legally admissible?
No. It has no legal standing whatsoever and is an educational estimate only.
Is this blood alcohol calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.