Cortisol nmol/L To ug/dL Converter
Convert cortisol laboratory results between nmol/L and ug/dL, with optional reference range conversion and clear notes on why unit conversion is not a medical interpretation.
Convert A Cortisol Result
Converted Result
This tool changes units only. It does not diagnose adrenal, pituitary or stress-related conditions, and it does not replace advice from a clinician or the laboratory that issued the report.
What This Converter Does
Some cortisol reports use SI units, usually nmol/L in the UK. Other reports, journal articles or overseas laboratories may use ug/dL. The two numbers can look very different even when they describe the same concentration. This converter changes the unit format while keeping the same cortisol amount. It is useful when comparing a report with a referral letter, checking a published study, completing a form or reading older notes that use conventional units.
The converter does not decide whether the result is clinically expected for your test. Cortisol varies by time of day, medicines, pregnancy, acute illness, stress, test method and the type of sample taken. A morning blood result, a late-night salivary result and a stimulation test result should not be compared as if they were the same test. Always use the reference interval printed by the laboratory for that sample and test protocol.
Formula And Factor
ug/dL = nmol/L / 27.586nmol/L = ug/dL x 27.586The factor is based on cortisol molecular mass of about 362.46 g/mol.1 ug/dL = 10 ug/L, then mass concentration is converted to molar concentration using molecular mass.Most laboratory conversion tables round the factor to 27.6 or 27.59. This tool uses 27.586 for calculation, then rounds the displayed answer according to your decimal-place setting. Small differences in the last decimal are usually just rounding, not a biological change.
Quick Conversion Table
| nmol/L | ug/dL | Use note |
|---|---|---|
| 50 | 1.81 | Unit conversion only. |
| 100 | 3.63 | Compare with the issuing laboratory range. |
| 150 | 5.44 | Check sample time and test type. |
| 250 | 9.06 | Same concentration, different unit. |
| 300 | 10.87 | Common example value for conversion practice. |
| 500 | 18.13 | Interpretation depends on context. |
| 750 | 27.19 | Use the report reference interval. |
| 1000 | 36.25 | Do not compare across test protocols without advice. |
Worked Examples
UK Report To US Unit
A report showing 300 nmol/L converts to 10.87 ug/dL. The converted number is not a new test result; it is the same result shown in another unit.
US Unit To UK Unit
A result of 10 ug/dL converts to 275.86 nmol/L. If a letter rounds this to 276 nmol/L, the difference is rounding only.
Reference Range Copying
If a report gives 150 to 500 nmol/L, enter both limits to convert the range to 5.44 to 18.13 ug/dL using the same factor.
How To Read A Converted Result Safely
Keep the original report unit visible when sharing a result. Many errors happen when a copied number loses its unit, or when a salivary result is compared with a blood reference interval. If you send the converted value to a clinician, include the original value, unit, sample type, date, collection time, medicines and the laboratory reference interval.
Do not use a search result or a different laboratory’s interval to judge your report. Assays and protocols vary. If symptoms are worrying, if the result is part of a stimulation or suppression test, or if steroid medicines are involved, ask the clinician who ordered the test how the result should be read.
Common Mistakes To Avoid
- Mixing nmol/L and ug/dL in the same note without labels.
- Comparing morning blood cortisol with late-night saliva cortisol.
- Using a reference interval from a different laboratory or a different sample type.
- Treating a rounded conversion difference as a real change in cortisol.
- Ignoring medicines such as steroid tablets, creams, inhalers or injections when discussing the result.
If you are preparing a message for a clinic, include the full line from the report rather than only the converted number. A useful note includes the original value, converted value, unit, sample type, collection time, date, medicines and the laboratory range. That gives the reviewer enough context to spot unit mistakes quickly.
Why Time And Test Type Matter
Cortisol is often linked to a clock time or a specific test protocol. A single morning sample, a late-night salivary sample, a dexamethasone suppression test and an ACTH stimulation test answer different clinical questions. The conversion factor is the same because the chemical is the same, but the meaning of the result comes from the protocol. Keep the protocol name beside the unit conversion when copying results into a personal record.
FAQs
What is the cortisol nmol/L to ug/dL conversion?
Divide nmol/L by 27.586. For example, 300 nmol/L is 10.87 ug/dL.
How do I convert ug/dL to nmol/L?
Multiply ug/dL by 27.586. For example, 10 ug/dL is 275.86 nmol/L.
Can this tell me whether my cortisol is high or low?
No. It converts units only. Use the laboratory reference interval and ask the clinician who requested the test.
Does the same factor work for saliva and urine?
The mass-to-molar unit factor is the same for cortisol, but sample type and reference interval are different. Compare only with the correct sample guidance.
Why do some tables use 27.6?
They round the factor. This page uses 27.586 and then rounds the displayed answer.
Sources
- Lab Tests Online UK. (2026). Cortisol test. The Association for Laboratory Medicine. https://labtestsonline.org.uk/tests/cortisol-test
- Unified Code for Units of Measure. (2024). UCUM specification. Regenstrief Institute. https://ucum.org/ucum
- National Library of Medicine. (2026). Unified Code for Units of Measure service. NLM. https://ucum.nlm.nih.gov/
- National Center for Biotechnology Information. (2026). PubChem Compound Summary for Cortisol. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Cortisol