Cortisol Units Converter
Convert a serum cortisol result between µg/dL and nmol/L instantly. Enter your lab value, pick the unit and sampling time, and see the equivalent result with typical reference ranges.
Convert Your Cortisol Result Between µg/dL and nmol/L
Cortisol Units Formula
Where:
- \(\text{µg/dL}\) — micrograms per deciliter, the unit commonly used for cortisol in the United States
- \(\text{nmol/L}\) — nanomoles per liter, the SI unit used in most of Europe, Canada and elsewhere
- \(27.59\) — the conversion factor derived from the molecular weight of cortisol (362.46 g/mol)
The factor 27.59 converts a mass concentration into a molar concentration: since 1 µg/dL of cortisol equals 10 mg/L, dividing by the molecular weight 362.46 g/mol gives 0.02759 µmol/L, i.e. 27.59 nmol/L.
Cortisol Units – Calculation Example
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Example: a morning lab report shows a serum cortisol of 12.5 µg/dL and you want the value in nmol/L.
\[ \text{cortisol (nmol/L)} = 12.5 \times 27.59 = 344.9 \approx 345 \]
Result: 12.5 µg/dL = 345 nmol/L (12.5 µg/dL), which lies within the typical morning reference range of 6–23 µg/dL (165–635 nmol/L).
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How to use the calculator
- Enter your Cortisol concentration exactly as printed on the lab report (e.g. 12.5).
- Select the unit of your report — µg/dL or nmol/L — in the dropdown next to the input field.
- Choose the Sampling time: Morning (6–8 a.m.) or Afternoon (4–6 p.m.). This is used only to compare your result with typical reference ranges.
- Read the results: your value expressed in both µg/dL and nmol/L, plus a short interpretation against typical ranges for the selected time of day.
What is cortisol and why do two units exist?
Cortisol is a steroid hormone produced by the adrenal glands. It regulates metabolism, blood pressure, immune responses and the body's response to stress. Because it is so central to health, cortisol is measured in blood, saliva and urine to investigate symptoms such as fatigue, weight changes, high blood pressure or abnormal blood sugar.
Laboratories report cortisol either as a mass concentration — micrograms per deciliter (µg/dL), the convention in the United States — or as a molar concentration — nanomoles per liter (nmol/L), the SI convention used in most other countries. The two scales differ by a factor of about 27.6, so a value that looks "high" in one unit can look deceptively "normal" in the other if read against the wrong reference range. Converting between the units lets you compare results from different labs or read international literature correctly.
The conversion is straightforward because cortisol is a single pure substance with a known molecular weight of 362.46 g/mol. Every µg/dL therefore always corresponds to exactly 27.59 nmol/L — no individual factors apply, unlike some other hormones reported in different molecular forms (see our Testosterone Units converter for an example).
Interpreting the result
A single cortisol value must always be read against the time of day the blood was drawn, because cortisol follows a strong circadian rhythm: it peaks shortly after waking and falls to roughly half by late afternoon. Typical adult morning ranges are about 6–23 µg/dL (165–635 nmol/L); in the late afternoon about 2–13 µg/dL (55–359 nmol/L). A morning result of 15 µg/dL is unremarkable, but the same value drawn at 5 p.m. would be above the usual afternoon range.
Mildly elevated values are common and often temporary — stress, pain, illness, intense exercise, pregnancy, oral estrogen or alcohol can all raise measured cortisol. Persistently high or very high values may point to Cushing syndrome and warrant further testing. Low morning cortisol can follow recent steroid medication use or, less commonly, indicate adrenal insufficiency. In all cases, a single measurement is not diagnostic: proper evaluation involves additional tests such as ACTH measurement or dexamethasone suppression testing, interpreted by a clinician.
Assumptions, limitations and practical tips
- The calculator uses the exact factor 27.59 (cortisol molecular weight 362.46 g/mol), so conversions are valid for serum, plasma and salivary cortisol reported in mass-per-volume units.
- Reference ranges shown are typical adult values only. Actual ranges vary between laboratories, assays and age groups — always use the range printed on your own lab report when available.
- Urine free cortisol is usually reported in µg/24 h and saliva in ng/mL; those results cannot be converted with this tool.
- The sampling time you select affects only the interpretation, not the conversion itself.
- This tool is for information only and is not a medical diagnosis. Discuss abnormal or unexpected results with your healthcare provider.
If you are comparing other lab reports across unit systems, you may also find our Creatinine Units converter, Cholesterol Units converter and HbA1c converter useful.
Frequently Asked Questions
How do I convert cortisol from µg/dL to nmol/L by hand?
Multiply the µg/dL value by 27.59. For example, \(10 \times 27.59 = 276\) nmol/L. To go the other way, divide the nmol/L value by 27.59 (or multiply by about 0.036): \(500 \div 27.59 \approx 18.1\) µg/dL. The factor comes from cortisol's molecular weight of 362.46 g/mol, so it is the same everywhere — there are no lab-specific conversion factors.
What is a normal cortisol level in µg/dL and nmol/L?
Typical adult morning (6–8 a.m.) serum cortisol is about 6–23 µg/dL, which equals roughly 165–635 nmol/L. In the late afternoon (4–6 p.m.) values fall to about 2–13 µg/dL (55–359 nmol/L) because cortisol follows a strong daily rhythm. Your own lab's reference range should take priority, since ranges vary between assays and laboratories. A single out-of-range result is not diagnostic — discuss it with your clinician.
Why can a normal cortisol result look 'high' or 'low' by mistake?
A common error is reading a value against a reference range in the wrong unit. Because 1 µg/dL equals about 27.59 nmol/L, the numbers differ by a factor of nearly 30. For instance, 10 µg/dL looks similar to 10 nmol/L as a number, but 10 nmol/L is a very low cortisol (about 0.36 µg/dL), while 10 µg/dL is a normal morning value (about 276 nmol/L). Always check the unit printed on the report first.
Can I use this converter for salivary or urine cortisol results?
No. This tool handles serum and plasma cortisol reported in µg/dL or nmol/L. Salivary cortisol is usually reported in ng/mL (or nmol/L with different reference ranges), and 24-hour urine free cortisol is reported in µg/24 h or nmol/24 h — a total amount, not a concentration. These cannot be converted with the serum factor, and their reference ranges are entirely different. Use the units and ranges printed on your specific report.
Does the conversion factor change between labs or countries?
No. Cortisol is a single pure molecule with a molecular weight of 362.46 g/mol, so 1 µg/dL always equals 27.59 nmol/L regardless of the laboratory, assay or country. This differs from hormones like testosterone, where results may be reported per different molecular forms. What does vary between labs is the reference range and the measurement method, so interpret your converted value against the range on your own report.
What does a low or high converted cortisol value mean?
High morning cortisol can reflect temporary stress, pain, illness, intense exercise, pregnancy, oral estrogen or alcohol, but persistently elevated values may suggest Cushing syndrome. Low morning cortisol can follow recent steroid medication use or, less commonly, point to adrenal insufficiency (Addison disease). Either way, diagnosis requires additional tests such as ACTH measurement or dexamethasone suppression testing, interpreted by a doctor — never rely on one number alone.
Do I need to convert cortisol when comparing with research papers or foreign lab reports?
Yes, whenever the units differ. US papers and labs typically use µg/dL, while European, Canadian, Australian and many other international sources use nmol/L. Convert your value to the same unit before comparing with a study's thresholds or ranges — for example, a midnight cortisol cutoff of 1.8 µg/dL equals about 50 nmol/L. This keeps you from misjudging whether a value is inside or outside a given range.