How to Convert Ethanol mg/dL to mmol/L
Blood alcohol is reported in mg/dL (US labs and legal BAC) and in mmol/L in many other countries. The conversion factor is 0.2171 (one mmol/L equals 4.61 mg/dL), from ethanol's molecular weight of 46.07 g/mol.
Ethanol mmol/L = ethanol mg/dL × 0.2171 BAC % = ethanol mg/dL ÷ 1000 (so 80 mg/dL = 0.08%) Ethanol mg/dL to mmol/L Chart
| mg/dL | mmol/L | Context |
|---|---|---|
| 50 mg/dL | 10.9 mmol/L | 0.05% — mild impairment |
| 80 mg/dL | 17.4 mmol/L | 0.08% — US legal driving limit |
| 100 mg/dL | 21.7 mmol/L | 0.10% |
| 200 mg/dL | 43.4 mmol/L | 0.20% — marked intoxication |
| 300 mg/dL | 65.1 mmol/L | 0.30% — stupor |
| 400 mg/dL | 86.8 mmol/L | 0.40% — potentially fatal |
mmol/L to mg/dL Reverse Chart
| mmol/L | mg/dL |
|---|---|
| 10 mmol/L | 46 mg/dL |
| 17.4 mmol/L | 80 mg/dL |
| 21.7 mmol/L | 100 mg/dL |
| 50 mmol/L | 230 mg/dL |
BAC Percentage, mg/dL and mmol/L
The three ways the same blood alcohol level is expressed:
| BAC % | mg/dL | mmol/L |
|---|---|---|
| 0.05% | 50 mg/dL | 10.9 mmol/L |
| 0.08% | 80 mg/dL | 17.4 mmol/L |
| 0.10% | 100 mg/dL | 21.7 mmol/L |
| 0.30% | 300 mg/dL | 65.1 mmol/L |
In most US states the driving limit is 0.08% (80 mg/dL, 17.4 mmol/L); many countries use 0.05% or lower. Effects rise with level, but tolerance varies widely between individuals.
Serum/Plasma vs Whole-Blood Alcohol
One important caveat: a hospital laboratory usually measures serum or plasma ethanol, which runs roughly 10–15% higher than the whole-blood alcohol used in legal testing. So a lab value should not be treated as a legal BAC.
Worked Example
Suppose a report shows 21.7 mmol/L and you want mg/dL:
21.7 × 4.61 = 100 mg/dL (0.10% BAC) Converting the other way, the 0.08% legal limit of 80 mg/dL is about 17.4 mmol/L.
Frequently Asked Questions
How do you convert ethanol mg/dL to mmol/L?
Multiply mg/dL by 0.2171. For example, 80 mg/dL is about 17.4 mmol/L.
How does mg/dL relate to BAC %?
Divide mg/dL by 1000: 80 mg/dL = 0.08%.
What is the legal driving limit?
0.08% (80 mg/dL, 17.4 mmol/L) in most US states; 0.05% in many countries.
Is lab ethanol the same as legal BAC?
No — serum/plasma runs ~10–15% higher than whole-blood BAC.
References
- Medscape — Ethanol Level: Reference Range and Interpretation.
- Ethanol factor 0.2171 (1 mmol/L = 4.61 mg/dL; MW 46.07 g/mol); BAC % = mg/dL ÷ 1000.
Conclusion
Converting ethanol between mg/dL, mmol/L and BAC percentage is straightforward: ×0.2171 for mmol/L, ÷1000 for percent. Just remember a laboratory serum value is not a legal whole-blood BAC.