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Blood alcohol in two units: the short answer
To convert blood alcohol from mg/dL to mmol/L, multiply by 0.2171. To go back from mmol/L to mg/dL, multiply by 4.606 (or divide by 0.2171). For example, 100 mg/dL × 0.2171 = 21.7 mmol/L. The converter above works in both directions and shows where the result sits against typical reference ranges.
What the test measures
Hospitals report blood ethanol in mg/dL in the US and mmol/L in the UK, Australia and elsewhere; legal limits use BAC percent or mg per 100 mL. Ethanol's molar mass is 46.07 g/mol, so 1 mg/dL = 0.2171 mmol/L. Also, 100 mg/dL = 0.10% BAC = 100 mg/100 mL.
Why the units differ
Medical reports and legal limits use different units, and hospital serum results are about 10–20% higher than whole-blood values used for legal BAC, so a direct comparison needs care.
Where the factor comes from
The conversion factor comes from the molar mass (46.07 g/mol) and the volume units on each side. Laboratories may round the factor slightly differently, which can change the last digit but never the clinical meaning.
How to convert step by step
- Check the unit printed next to the result on your report – mg/dL or mmol/L.
- mg/dL → mmol/L: multiply by 0.2171.
- mmol/L → mg/dL: multiply by 4.606.
- Round to the same number of decimals your lab uses.
Worked example in reverse: 10.9 mmol/L × 4.606 = 50.2 mg/dL.
Blood alcohol conversion chart
| mg/dL | mmol/L |
|---|---|
| 10 | 2.2 |
| 20 | 4.3 |
| 50 | 10.9 |
| 80 | 17.4 |
| 100 | 21.7 |
| 150 | 32.6 |
| 200 | 43.4 |
| 300 | 65.1 |
| 400 | 86.8 |
| mmol/L | mg/dL |
|---|---|
| 2.2 | 10.1 |
| 4.3 | 19.8 |
| 10.9 | 50.2 |
| 17.4 | 80.1 |
| 21.7 | 100 |
| 32.6 | 150.2 |
| 43.4 | 199.9 |
| 65.1 | 299.9 |
| 86.8 | 399.8 |
Blood alcohol levels: what the numbers mean
| Category | mg/dL | mmol/L |
|---|---|---|
| US driving limit (whole blood)0.08% BAC ≈ 17.4 mmol/L | ≥ 80 | ≥ 17.4 |
Legal limits vary by country and are defined on whole blood or breath. Hospital serum ethanol is not directly equivalent.
Legal limits vary by country and are defined on whole blood or breath. Hospital serum ethanol is not directly equivalent.
Interpreting blood alcohol results
Ethanol is cleared at roughly 15–20 mg/dL per hour in most adults, faster in some heavy drinkers. The same level affects people differently: tolerance, other drugs and illness change how impaired someone is. Ethanol also raises serum osmolality, and the gap between measured and calculated osmolality is used to look for other toxic alcohols. This converter is for understanding results, not for judging whether it is safe to drive.
A single result outside the reference range is common and often not significant on its own. Reference ranges are set so that about 1 in 20 healthy people fall outside them, and every laboratory sets its own limits for its method. Use the range printed on your report and discuss results with the clinician who ordered the test.
When to see a doctor
Contact your clinician if a result is flagged as abnormal and you have symptoms, if a value is far outside the range, or if results are changing over time. This page explains units; it cannot diagnose or replace medical advice.
Frequently asked questions
What is 0.08% BAC in mg/dL?
0.08% = 80 mg/dL (80 mg per 100 mL), about 17.4 mmol/L.
Is a hospital blood alcohol the same as a legal BAC?
Not exactly. Hospitals usually measure serum or plasma, which reads higher than whole blood. Legal tests use whole blood or breath.
Can I use this converter for any lab?
Yes for the unit conversion, which is fixed by chemistry. Reference ranges differ between labs and methods, so compare your converted value with your own lab's range.