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Blood alcohol calculator

Estimate your blood alcohol concentration (BAC) with the Widmark formula.

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Need Blood alcohol concentration, Hours to sober? The Blood alcohol calculator derives it from Sex, Weight (kg), Standard drinks, Grams of alcohol per drink, Hours since first drink in one step. For instance, with Sex = Male, Weight (kg) = 75, Standard drinks = 2, Grams of alcohol per drink = 14 and Hours since first drink = 1 it returns Blood alcohol concentration = 0.04 % BAC and Hours to sober = 2.66 h.

How to use it

  1. Enter your values: Sex, Weight (kg), Standard drinks, Grams of alcohol per drink, Hours since first drink.
  2. Read the result instantly: Blood alcohol concentration, Hours to sober.

Frequently asked questions

How does the Blood alcohol calculator work?

It takes Sex, Weight (kg), Standard drinks, Grams of alcohol per drink and Hours since first drink and derives Blood alcohol concentration and Hours to sober from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

5 values: Sex, Weight (kg), Standard drinks, Grams of alcohol per drink and Hours since first drink. Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Sex = Male, Weight (kg) = 75, Standard drinks = 2, Grams of alcohol per drink = 14 and Hours since first drink = 1, the calculator returns Blood alcohol concentration = 0.04 % BAC and Hours to sober = 2.66 h. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Sex = Female, Weight (kg) = 83, Standard drinks = 4, Grams of alcohol per drink = 28 and Hours since first drink = 2 instead, Blood alcohol concentration goes from 0.04 % BAC to 0.215 % BAC — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Sex” option should I choose?

You can pick between « Male » and « Female ». Each one changes what the calculator works out, so switch and compare — the default is « Male ».

What does it give for smaller values?

Scaled down to Sex = Male, Weight (kg) = 68, Standard drinks = 1, Grams of alcohol per drink = 7 and Hours since first drink = 0.5, Blood alcohol concentration comes out at 0.008 % BAC. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Checking one clinical number against the definition that gives it meaning: a dose against a body weight, a laboratory value corrected for the albumin or glucose that distorted it, a blood pressure against a guideline's threshold table, a heart rate or a basal metabolic rate against the formula that defines it.

What is the most common mistake?

Reading the output as a finding. Every figure here is arithmetic on numbers you typed: a correction formula measures nothing, and a threshold table classifies one reading rather than a person. Blood pressure in particular means little until it has been measured repeatedly on separate occasions, and a dose worked out here is a way of checking a prescription, never of writing one.

How accurate is it, and what are the limits?

Rough estimate only — actual BAC varies with metabolism, food, medication and other factors. NEVER use this figure to decide whether to drive. If you have been drinking, do not drive.

What is the difference between the Blood alcohol calculator and the Blood Donation Time Calculator?

This one returns Blood alcohol concentration and Hours to sober; the Blood Donation Time Calculator returns Result. That is the whole difference — open the one whose figure you need.

Further reading

All guides →
ExplainerHow Long Does Alcohol Stay in Your System?The body clears roughly one standard drink per hour. See how long alcohol stays in blood, breath and urine — and why you can't rush it.ExplainerWhat Is Blood Alcohol Content (BAC)?Blood alcohol content measures the concentration of alcohol in your blood. Learn how BAC is estimated with the Widmark formula and why legal limits differ by country.ExplainerWhat a Standard Drink Actually IsA standard drink is a defined mass of ethanol — and the definition changes at the border. The same glass of wine is 1.28 drinks in the United States, 1.79 in France and 2.28 in the United Kingdom.ExplainerHow Blood Type Is Inherited: The Full Parent-to-Child TableEach parent passes on one ABO allele — A, B or O — and Rh follows a separate gene. Here is every parent combination, which child types it can and cannot produce, and why this is not a paternity test.ExplainerCorrected Sodium, and Why Glucose Moves ItHigh blood glucose pulls water out of cells and dilutes the sodium in it, so a measured sodium in a hyperglycaemic patient reads lower than the real one. Here is the correction, both of the published factors, a case where they disagree by 4 mmol/L, and the different problem that lipids cause.ExplainerWeight-Based Dosing, and Where the Arithmetic Goes WrongMilligrams per kilogram is one multiplication, and that is exactly why it fails: the documented errors are unit slips, misplaced decimal points and the wrong body weight, not hard maths. Here is the arithmetic done properly, the three body weights that give three different answers, and what body surface area changes.