About

This tool converts alcohol concentration values between the two primary standards used in traffic safety and law enforcement: blood analysis (Promille, ‰) and breath analysis (mg/L). While blood tests measure the weight of ethanol in blood volume, breathalyzers measure ethanol vapor in exhaled air. The correlation between these two measurements relies on a partition coefficient, often referred to as the Blood-Breath Ratio (BBR).

Legislation varies significantly by jurisdiction regarding which measurement is definitive. Some legal systems apply a fixed conversion factor (typically 2000:1, 2100:1, or 2300:1) to translate breath readings into a blood-equivalent Promille value. Consequently, a reading of 0.25 mg/L might legally equate to 0.50 ‰ in France but 0.525 ‰ in Germany. Precision is critical when evaluating compliance with local DUI/DWI statutes.

Disclaimer: This calculator provides mathematical conversions based on standard legislative ratios. It does not account for individual metabolic rates, body temperature, or hematocrit levels, all of which influence actual biological partition ratios. Do not use this tool to determine fitness to drive.

Formulas

The conversion relies on the Henry's Law constant established by local legislation. The standard formula relates the concentration in blood (C_blood) to the concentration in breath (C_breath) via a partition factor k.

C_blood ≈ C_breath × k1000

However, since Promille is expressed in grams per liter (roughly) and breath in milligrams per liter, the practical calculation simplifies using the Ratio Multiplier (R).

Promille (‰) = mg/L × R

Where R is derived from the partition ratio:

{

R = 2.0 for Ratio 2000:1 (France, Scandinavia)R = 2.1 for Ratio 2100:1 (Germany, USA)R = 2.3 for Ratio 2300:1 (UK)

Reference Data

Country / Region	Legal Limit (Blood)	Legal Limit (Breath)	Implied Factor (Ratio)
Germany	0.5 ‰	0.25 mg/L	2100:1 (×2.1)
France	0.5 ‰	0.25 mg/L	2000:1 (×2.0)
Poland	0.2 ‰	0.10 mg/L	2100:1 (×2.1)
Netherlands	0.5 ‰	0.22 mg/L	~2272:1 (×2.27)
United Kingdom (England/Wales)	0.8 ‰ (80mg/100ml)	0.35 mg/L (35µg/100ml)	2300:1 (×2.3)
United Kingdom (Scotland)	0.5 ‰ (50mg/100ml)	0.22 mg/L (22µg/100ml)	2300:1 (×2.3)
Sweden	0.2 ‰	0.10 mg/L	2000:1 (×2.0)
Norway	0.2 ‰	0.10 mg/L	2000:1 (×2.0)
Spain	0.5 ‰	0.25 mg/L	2000:1 (×2.0)
Austria	0.5 ‰	0.25 mg/L	2000:1 (×2.0)
Italy	0.5 ‰	0.25 mg/L (Est.)	2000:1 (×2.0)
Finland	0.5 ‰	0.22 mg/L	~2272:1 (×2.27)
USA (General)	0.08 % (0.8 ‰)	0.38 mg/L (varies)	2100:1 (×2.1)

Frequently Asked Questions

BAC (Blood Alcohol Concentration) measures the weight of alcohol in a specific volume of blood, typically expressed in Promille (‰) or percentages (%). BrAC (Breath Alcohol Concentration) measures the weight of alcohol in exhaled air, usually in mg/L or µg/100ml. While BAC is the "gold standard" for medical toxicity, BrAC is the standard for roadside police enforcement due to the non-invasive nature of breathalyzers.

The physiological ratio of alcohol in blood to breath varies between individuals (typically ranging from 1900:1 to 2400:1). Legislators must choose a single legal standard to apply to everyone. Countries like France and Austria use a lower 2000:1 ratio to be more favorable to the driver (underestimating blood alcohol), while the USA and Germany typically use 2100:1 as a statistical average.

It depends on the jurisdiction. In a country using the 2000:1 ratio (factor 2.0), yes, 0.25 mg/L multiplied by 2.0 equals 0.50 Promille. However, in a country using the 2100:1 ratio (factor 2.1), 0.25 mg/L equates to 0.525 Promille, which might technically exceed a strict 0.5 limit if the law is written based on blood value.

No. This tool provides theoretical conversions based on statutory limits. Real-world legal cases involve calibrated hardware, margins of error (often subtracted from the reading by police), and specific local case law. Always consult a lawyer regarding legal charges.

The UK often uses micrograms per 100 milliliters of breath (µg/100ml). To convert this to the standard European mg/L: divide the UK value by 100. For example, the limit of 35 µg/100ml equals 0.35 mg/L.