Converting mg/100ml to BAC: The Forensic Science Guide
Blood alcohol concentration can be expressed in several different units depending on the country and legal context. Converting between mg/100ml, g/L, ‰ promille, and BAC% is essential for understanding international driving laws, breathalyzer readings, and forensic reports.
The Alcomato BAC calculator uses % BAC. Use this guide to convert any other unit.
Calculate Your BAC Now →The Different Units of Blood Alcohol Measurement
| Unit | What it means | Used in |
|---|---|---|
| % BAC (g/dL) | Grams of alcohol per 100mL of blood | USA, Canada |
| mg/100mL | Milligrams per 100mL of blood (= same as %BAC × 1000) | UK (blood tests) |
| mg/dL | Same as mg/100mL | Medical labs |
| mmol/L | Millimoles per liter (ethanol MW = 46.07 g/mol) | Some medical contexts |
| g/L | Grams per liter | France, WHO |
| Promille (‰) | Grams per 1000mL (= g/L) | Germany, Poland, Eastern Europe |
| μg/100mL (breath) | Micrograms per 100mL of breath | UK breathalyzer |
Conversion Formulas
All conversions from % BAC as the reference:
| To convert from % BAC to... | Formula | Example (0.08% BAC) |
|---|---|---|
| mg/100mL | × 100 | 80 mg/100mL |
| mg/dL | × 100 | 80 mg/dL |
| g/L | × 10 | 0.8 g/L |
| Promille (‰) | × 10 | 0.8‰ |
| mmol/L | × 10 / 46.07 × 1000 | 17.4 mmol/L |
| μg/100mL breath | × 2174 (approx) | ~174 μg/100mL |
The breath-to-blood conversion uses a partition ratio of approximately 2100:1 (blood:breath), though the UK legal standard uses 2300:1 for calculation of the 35 μg/100mL breath limit.
Use Alcomato's BAC calculator for your personal blood alcohol estimate.
Calculate Your BAC Now →Complete Conversion Reference Table
| % BAC | mg/100mL | g/L (‰) | mmol/L | Impairment level |
|---|---|---|---|---|
| 0.02% | 20 mg/100mL | 0.2 g/L | 4.3 mmol/L | Mild — Poland admin offense |
| 0.04% | 40 mg/100mL | 0.4 g/L | 8.7 mmol/L | Moderate impairment begins |
| 0.05% | 50 mg/100mL | 0.5 g/L | 10.9 mmol/L | EU legal limit (most countries) |
| 0.08% | 80 mg/100mL | 0.8 g/L | 17.4 mmol/L | USA/UK legal limit |
| 0.10% | 100 mg/100mL | 1.0 g/L | 21.7 mmol/L | Serious impairment |
| 0.15% | 150 mg/100mL | 1.5 g/L | 32.6 mmol/L | Aggravated DUI threshold (many states) |
| 0.20% | 200 mg/100mL | 2.0 g/L | 43.4 mmol/L | Very high intoxication |
| 0.30% | 300 mg/100mL | 3.0 g/L | 65.2 mmol/L | Life-threatening |
| 0.40% | 400 mg/100mL | 4.0 g/L | 86.9 mmol/L | Potentially fatal |
UK Breathalyzer System Explained
The UK uses a unique dual system: blood tests measure mg/100mL (legal limit: 80 mg/100mL = 0.08% BAC), while roadside breathalyzers measure micrograms per 100mL of breath (legal limit: 35 μg/100mL). The relationship between breath and blood alcohol is approximately 1:2300 (UK legal standard).
Frequently Asked Questions
What does 50 mg/100mL mean in BAC%?
50 mg/100mL = 0.05% BAC. This is the legal driving limit in most EU countries, including Germany, France, Poland (criminal threshold), Australia, and many others.
Is 80 mg/100mL the same as 0.08%?
Yes, exactly. 80 mg/100mL = 80 mg per 100mL = 0.08g per 100mL = 0.08% (grams per deciliter). The US, UK, and Canadian legal limits are expressed differently but mean the same concentration.
What is 0.08% BAC in mmol/L?
0.08% BAC = 0.8 g/L. Ethanol molecular weight = 46.07 g/mol. So: 0.8 g/L ÷ 46.07 g/mol × 1000 = 17.4 mmol/L.
Disclaimer: This article is for educational purposes only and does not constitute legal or medical advice. BAC estimates are approximations. Individual results vary based on body composition, food intake, health status, and other factors. Never drive if you feel impaired. When in doubt, don’t drive.