Cortisol Conversion Chart | Clear Unit Math

Use 27.59 to switch between serum µg/dL and nmol/L cortisol, then match the lab’s specimen and time window before you read ranges.

A cortisol report can look simple until the units don’t match what you expected. One lab prints µg/dL, another prints nmol/L, and a third gives urine totals for a full day. That mismatch can turn a routine result into a guessing game.

This page fixes that. You’ll get the exact conversion factors that labs use, a chart you can copy, and worked examples so you can sanity-check your math. You’ll also see the traps that cause bad comparisons, like mixing serum and saliva numbers or comparing a morning draw to an all-day urine collection.

What Cortisol Units Mean In Real Reports

Cortisol can be measured in blood, saliva, or urine. The sample type matters because the number you see is shaped by where cortisol is carried and how it moves in the body. MedlinePlus’ cortisol test overview notes that testing can use blood, urine, or saliva, and that timing across the day is part of how results are gathered.

Most blood tests report a concentration: how much cortisol is in a given volume of blood. That shows up as micrograms per deciliter (µg/dL) in many U.S. labs and nanomoles per liter (nmol/L) in many SI-unit labs.

Urine tests often report a total amount collected over a fixed period, most often 24 hours. That shows up as micrograms per 24 hours (µg/24 h) or nanomoles per 24 hours (nmol/24 h). A urine total is not the same thing as a blood concentration, so converting units won’t make the test types comparable.

Mass Units Vs Mole Units

µg/dL is a mass unit. It answers “How many micrograms of cortisol are in each deciliter of sample?”

nmol/L is a mole unit. It answers “How many cortisol molecules are present per liter?” The bridge between mass and moles is cortisol’s molecular weight, which lab catalogs list near 362.5 g/mol for conversion work.

Why Timing Changes The Story

Cortisol follows a daily rhythm. That’s why lab orders often spell out a draw time, and why many saliva panels call for more than one sample. If you compare a 8–9 a.m. blood draw to a late-day draw, a “difference” may just be normal timing.

When A Cortisol Conversion Helps, And When It Doesn’t

Unit conversion is useful when:

• You have the same specimen type and the same timing, but the units differ (µg/dL vs nmol/L, or µg/24 h vs nmol/24 h).
• You’re reading a paper or lab note written in SI units while your report uses conventional units, or the other way around.
• You need to double-check a calculation in a note that lists a value in one unit and a reference range in another.

Unit conversion is not useful when:

• You’re trying to compare blood cortisol to urine free cortisol, or saliva to serum.
• You’re comparing numbers from different assay methods without a lab note that they’re aligned.
• You’re comparing values collected at different times of day.

For medical decisions, labs and clinicians rely on the reference range that matches that specific test method and collection timing. The Mayo Clinic Laboratories SI unit conversion page is a handy reference for switching units, but interpretation still needs to match the ordered test and its reference interval.

How To Convert Serum Cortisol Step By Step

Most people need one conversion: serum µg/dL ↔ nmol/L.

• µg/dL to nmol/L: multiply by 27.59.
• nmol/L to µg/dL: divide by 27.59.

That 27.59 factor comes from cortisol’s molecular weight and the deciliter-to-liter shift. Labs may print 27.6 due to rounding, which works fine for daily reading.

Worked Example: µg/dL To nmol/L

Your report: 14 µg/dL.

Math: 14 × 27.59 = 386.26 nmol/L.

Rounded the way many reports show it: 386 nmol/L.

Worked Example: nmol/L To µg/dL

Your report: 500 nmol/L.

Math: 500 ÷ 27.59 = 18.12 µg/dL.

Rounded: 18.1 µg/dL.

Common Display Units You Might See

Some portals show µg/L or nmol/L side by side. If you see µg/L for serum, note that 1 dL is 0.1 L, so µg/dL is 10× µg/L. That’s not a new hormone value, just a volume swap.

Cortisol Conversion Chart For Lab Units And Reports

Use this chart when the specimen type matches and you only need to switch units. If the report is a 24-hour urine test, stick to the urine rows. If the report is serum, stick to the serum rows.

The 2.76 urine factor is published in lab catalogs for urinary free cortisol and is tied to cortisol’s molecular weight. One example is the University of Vermont Medical Center Laboratories urinary free cortisol catalog entry, which prints the conversion and the molecular-weight basis.

Urine, Saliva, And Serum: Don’t Mix These Numbers

A single “cortisol number” can mean different things depending on the sample.

Serum Or Plasma Cortisol

This is a concentration at a point in time. It’s often used in testing for adrenal insufficiency or in stimulation testing, where timing is part of the protocol.

Late-Night Salivary Cortisol

This is a free cortisol measure at night. It’s used in screening steps because it samples a time when cortisol is normally low. The Endocrine Society’s Cushing’s syndrome guideline resources list late-night salivary cortisol and urinary free cortisol as common initial tests used in screening for excess cortisol states.

Urinary Free Cortisol Over 24 Hours

This totals cortisol excreted across the full collection. Since it pools a day, it isn’t shaped by the morning peak in the same way as a single blood draw. A lab catalog will give its own reference interval for that method, plus the conversion factor to nmol/24 h.

What Reference Ranges Can And Can’t Tell You

It’s tempting to hunt for a single “normal cortisol” number. Real reports don’t work that way. Reference intervals depend on specimen type, collection time, and lab method.

Use the range printed next to your result as your first anchor. If you’re reading a range from a paper or a different lab, convert units only after you verify that it’s the same test type and timing.

If your result is flagged high or low, that flag is tied to that lab’s interval, not a universal cutoff. If symptoms or test results worry you, contact a clinician. Extra testing is common because cortisol shifts across the day and can be affected by many meds and health states.

Common Conversion Mistakes That Skew Comparisons

• Using the serum factor on a urine total. Serum uses 27.59; 24-hour urine totals use 2.76 when you move from µg/24 h to nmol/24 h.
• Dropping the time window. “AM cortisol” and “PM cortisol” are not interchangeable labels.
• Mixing mg and µg. 1 mg equals 1000 µg. One missing symbol can blow up the number.
• Confusing dL with L. A deciliter is one-tenth of a liter, so a unit shift can add or remove a zero.
• Rounding too early. Keep one or two decimals in the middle of the math, then round at the end.

Quick Cross-Checks You Can Do In Your Head

These mental checks catch most typos:

• If you convert µg/dL to nmol/L, the number should get larger by a lot. One digit changes into a few hundred.
• If you convert nmol/L to µg/dL, the number should drop into the teens or single digits for many routine values.
• If you convert µg/24 h to nmol/24 h, the number should rise, but not as sharply as serum conversion. The factor is 2.76, not 27.59.

Second Chart: Serum And Urine Conversions With Examples

This table pairs common report formats with the exact math. Use it as a plug-and-play template when you’re reading a portal or a study.

How Labs Label Units, And Why It Matters

Some portals shorten symbols or swap “mcg” for “µg.” Treat mcg and µg as the same unit. A portal may also swap “dL” with “100 mL.” That’s the same volume, so µg/dL and µg/100 mL match.

Urine tests can list “per day,” “per 24 h,” or “per 24 hours.” In most clinical catalogs, these labels point to the same 24-hour collection window. Still, the safest move is to read the collection instructions on the order.

A Simple Checklist Before You Compare Two Cortisol Results

• Check specimen type: serum, saliva, or urine.
• Check timing: morning draw, late-day draw, late-night saliva, or 24-hour urine.
• Check units: µg/dL, nmol/L, µg/24 h, nmol/24 h, or another label.
• Convert units only after the first two items match.
• Use the reference interval that matches the exact test on the report.
• If you’re tracking results across labs, ask the clinician ordering the tests whether the assay methods match.

When To Seek Medical Help

Cortisol testing can be part of workups for adrenal insufficiency and excess cortisol states, and it often takes more than one test because cortisol varies across the day. If your report is flagged out of range, or if you feel unwell and the result raises questions, reach out to a clinician. If you have urgent symptoms like fainting, severe weakness, or confusion, seek urgent care.

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