Both directions
Start from a blood result or a breath reading, then choose independent input and output units.
BAC–BrAC converter
Alcohol in blood and breath
Convert in either direction and choose a country to apply the relationship used by that legal system. Detection suggests a country, but you can change it before travelling.
Legal system
Convert using the relevant local relationship
Legal system: …
Finding the reference country…
Finding the reference country and the right units…
Country changes the relationship
The UK, US and many metric systems do not express the same legal BAC–BrAC relationship in the same way.
An equivalent, not a measurement
Blood and breath are different samples. A calculated relationship cannot replace a blood analysis or a maintained breathalyzer.
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Reading the result
Choose the country before interpreting the number
Converting between units within blood or within breath is arithmetic. Moving between blood and breath requires a chosen BAC–BrAC relationship, so the calculator shows the selected country, reference pair and source.
If no confirmed legal pair is available, the result uses the technical 2100:1 relationship and is clearly marked as non-local. It is not a legal threshold or evidence of fitness to drive.
Frequently asked questions
Does 0.05% BAC always equal 0.25 mg/L breath?
No. Some systems use a relationship close to that pair, while others define a different legal equivalent. The individual blood-to-breath relationship also changes over time and differs between people.
Why does the United Kingdom have two variants?
Scotland uses 50 mg/100 mL blood and 22 µg/100 mL breath. England, Wales and Northern Ireland use 80 mg/100 mL and 35 µg/100 mL.
Does the result mean I can drive?
No. It is only an approximate numeric equivalent. Law has exceptions, devices have uncertainty and alcohol can impair driving below a statutory threshold. If you have been drinking, do not drive.
Sources and conversion coverage
The source for the currently selected country appears directly beside the relationship used above the calculator. The broader sources below support the database and the technical fallback conversion.
We create a country profile only when a source gives a numeric blood value and breath value side by side, or states an unambiguous factor used by that system. The WHO table provides a technical reference, but on its own it does not determine the legal conversion factor for a particular country.
- World Health Organization / IFRC: Drink driving: a road safety manual
A reference table linking BAC and BrAC values, including 0.50 g/L in blood and 0.24 mg/L in breath. The manual notes that legal definitions and testing rules differ between countries.
- International Alliance for Responsible Drinking (IARD): Blood Alcohol Concentration (BAC) Limits
A comparison of national BAC and BrAC values checked against national authorities or public documents.
- National Highway Traffic Safety Administration: Alcohol Measurement and Enforcement
Explains the US relationship between grams per 210 litres of breath and grams per decilitre of blood, as well as the limitations of conversion.
This is educational information, not legal or medical advice. Check current local rules before travelling. Never use a calculated result as the basis for deciding to drive.
