Units
Ferritin units explained: ng/mL, µg/L and pmol/L
Ferritin is printed in different units depending on the laboratory. Here is how ng/mL, µg/L and pmol/L relate, with the conversion factors and a worked example.
By FerroLady · Updated · 4 min read
Two laboratories can measure the same sample and print the number differently, because they use different units. Ferritin is a common example. A result might read ng/mL on one report and µg/L on another, and a few laboratories print pmol/L.
ng/mL and µg/L are the same quantity
One nanogram per millilitre is exactly one microgram per litre. A ferritin written as 40 ng/mL is the same as 40 µg/L. Laboratories in the United States usually print ng/mL, and laboratories in the United Kingdom and Australia usually print µg/L, so the digits carry over unchanged when you move between them.
Converting to pmol/L
Some laboratories report ferritin in picomoles per litre. The commonly used factor is 2.247, so:
- µg/L (or ng/mL) × 2.247 = pmol/L
- pmol/L ÷ 2.247 = µg/L (or ng/mL)
For example, a value written as 40 µg/L is the same quantity as 89.9 pmol/L. Only the unit has changed, not what was measured.
Why the unit belongs next to the number
A bare number does not say which unit it is in, and the same digits in two different units are different quantities. Laboratories also publish their own reference ranges, and a range is written in the unit that laboratory uses. Writing the unit exactly as it is printed on the report, every time, keeps your own records unambiguous when you look back or show them to someone else.
How FerroLady handles units
FerroLady stores each value in the unit you typed and never converts what you saved. A number is never shown without its unit, on screen, in charts, or in the one-page report. It records ferritin in µg/L or ng/mL.
