Common values

nmol/L	µg/dL
25	0.9
50	1.8
83	3.0
100	3.6
138	5.0
170	6.2
200	7.2
276	10.0
300	10.9
400	14.5
450	16.3
500	18.1
540	19.6
600	21.7
700	25.4
800	29.0

How the conversion works

Cortisol has a molar mass of 362.46 grams per mole. A concentration of 1 µg/dL is 10 micrograms per litre, and 10 µg divided by 362.46 g/mol is 27.59 nanomoles. So to turn µg/dL into nmol/L, multiply by 27.59; to go the other way, divide by 27.59.

What the number means

A blood cortisol result only means something next to the time it was taken. Cortisol peaks in the morning, at around 8.30 in healthy people who sleep at night, and is lowest around midnight, so a morning result and an afternoon result from the same person can be very different. Laboratories set their own reference ranges, which also depend on the assay they use, so always compare your result with the range printed on your report. See normal cortisol levels and the blood cortisol test.

Hair results use different units

Hair cortisol is reported as picograms of cortisol per milligram of hair (pg/mg). It measures something different, the average over months rather than the level at one moment, so it cannot be converted into a blood value. See hair cortisol results explained.