Health & Fitness

Blood alcohol to breath alcohol conversion

Blood alcohol to breath alcohol conversion: calculation method, required inputs, worked check, limitations and a link to Blood Alcohol Calculator. Reviewed 2...

By Uddhav Gopani, FounderPublished 25 September 2026Reviewed 25 September 2026

For “Blood alcohol to breath alcohol conversion”, the linked Blood Alcohol Calculator is relevant because Estimate blood alcohol concentration with the Widmark formula — for education only, never for deciding whether to drive.

What this specific question is asking

Each input for this calculation has to mean the same thing on your side as it does in Blood Alcohol Calculator: check that body weight (kg), sex, number of drinks, drink size (ml), drink strength (abv %) and hours since first drink are entered in the units and periods the tool expects, then read the output with those same units attached.

Validate by perturbation: nudge body weight (kg) by ten percent and watch the output. A result that barely moves — or jumps wildly — usually means a wrong unit or period, not a broken formula.

Inputs to verify

Verify body weight (kg) before calculation; if this value uses a different unit, period or definition, convert or restate it first.
Verify sex before calculation; if this value uses a different unit, period or definition, convert or restate it first.
Verify number of drinks before calculation; if this value uses a different unit, period or definition, convert or restate it first.
Verify drink size (ml) before calculation; if this value uses a different unit, period or definition, convert or restate it first.
Verify drink strength (abv %) before calculation; if this value uses a different unit, period or definition, convert or restate it first.
Verify hours since first drink before calculation; if this value uses a different unit, period or definition, convert or restate it first.

Step-by-step check

Enter your body weight and select your sex.
Enter the number of drinks, their size in ml, and ABV %.
Enter hours since your first drink.
Press Calculate to see an educational BAC estimate.

Worked example and sanity check

As a worked reference for “Blood alcohol to breath alcohol conversion”, Worked example For a 70 kg man, two 355 ml drinks at 5% ABV is about 2 × 355 × 0.05 × 0.789 ≈ 28 g of alcohol. The Widmark estimate is 28 ÷ (70,000 g × 0.68) × 100 ≈ 0.059% before metabolism is subtracted. This is an educational estimate only — never use it to decide whether to drive.

Interpreting the result

Interpretation starts with magnitude. The worked example landed at about 2 × 355 × 0; compare yours before trusting the decimals. If the two disagree wildly, the setup — usually body weight (kg)'s unit or period — is the suspect. Treat the number as a screening estimate for orientation, not a diagnosis or a personalised prescription; individual measurement error and physiology dominate any formula's precision.

Reviewed 25 September 2026

Verify any current tax threshold, lender rate, provider rule or health guidance with the authoritative source before acting.

Use the Blood Alcohol Calculator

Open Blood Alcohol Calculator

Common questions

Which inputs matter most for blood alcohol to breath alcohol conversion?

The key inputs are Body weight (kg), Sex, Number of drinks, Drink size (ml). Match their units and periods before using Blood Alcohol Calculator.

How can I check an answer for blood alcohol to breath alcohol conversion?

Reproduce the worked example with its stated inputs first, then change body weight (kg) by a known amount and confirm the output moves the way the relationship predicts. Only then substitute your own values.

When should I recalculate blood alcohol to breath alcohol conversion?

Recalculate whenever any input's basis changes: a new measurement, a revised rate or threshold, a different period convention, or an updated policy figure.