How to Convert Acetaminophen µg/mL to µmol/L
Acetaminophen (paracetamol) levels are reported in µg/mL (mg/L) in the US and in µmol/L in many other countries. The conversion factor is 6.62, from its molecular weight of 151.16 g/mol.
Acetaminophen µmol/L = acetaminophen µg/mL × 6.62 Acetaminophen µg/mL = acetaminophen µmol/L ÷ 6.62 Acetaminophen µg/mL to µmol/L Chart
| µg/mL | µmol/L | Context |
|---|---|---|
| 10 µg/mL | 66 µmol/L | Therapeutic |
| 20 µg/mL | 132 µmol/L | Upper therapeutic |
| 50 µg/mL | 331 µmol/L | Elevated |
| 100 µg/mL | 662 µmol/L | High |
| 150 µg/mL | 993 µmol/L | Nomogram treatment line (4 h) |
| 300 µg/mL | 1986 µmol/L | Very high |
µmol/L to µg/mL Reverse Chart
| µmol/L | µg/mL |
|---|---|
| 66 µmol/L | 10.0 µg/mL |
| 132 µmol/L | 19.9 µg/mL |
| 660 µmol/L | 99.7 µg/mL |
| 993 µmol/L | 150.0 µg/mL |
The Rumack-Matthew Nomogram Treatment Line
For a single acute overdose, risk is judged against the treatment line, which starts at 150 µg/mL (993 µmol/L) at 4 hours after ingestion and falls to about 4.7 µg/mL (31 µmol/L) at 24 hours. A level on or above the line for its time point means N-acetylcysteine (NAC) is indicated.
| Time since ingestion | Treatment line (µg/mL) | µmol/L |
|---|---|---|
| 4 hours | 150 µg/mL | 993 µmol/L |
| 8 hours | 75 µg/mL | 496 µmol/L |
| 12 hours | 37.5 µg/mL | 248 µmol/L |
| 16 hours | 18.8 µg/mL | 124 µmol/L |
The nomogram only applies to a single ingestion with a known time, using a level drawn at least 4 hours after ingestion. Staggered or unknown-timing overdoses are assessed differently and always by a clinician or poison centre.
Worked Example
Suppose a report shows 660 µmol/L and you want µg/mL:
660 ÷ 6.62 = 99.7 µg/mL Whether that is above the treatment line depends entirely on the hours since ingestion. Converting the other way, 150 µg/mL is 993 µmol/L.
Frequently Asked Questions
How do you convert acetaminophen µg/mL to µmol/L?
Multiply µg/mL by 6.62. For example, 150 µg/mL is about 993 µmol/L.
What is the treatment line?
150 µg/mL (993 µmol/L) at 4 hours, falling to ~4.7 µg/mL (31 µmol/L) at 24 hours.
Is acetaminophen the same as paracetamol?
Yes — same drug, same 6.62 factor.
When is the level meaningful?
For a single ingestion, drawn at least 4 hours afterward.
References
- StatPearls / NCBI — Acetaminophen Toxicity.
- Acetaminophen factor 6.62 (MW 151.16 g/mol); Rumack-Matthew nomogram treatment line (150 µg/mL at 4 h).
Conclusion
Converting acetaminophen between µg/mL and µmol/L is a ×6.62. But in overdose the number only means something next to the time since ingestion and the nomogram — suspected overdose needs urgent professional assessment.