Iron result converter

UK labs report iron in micromoles, US sites in micrograms. Convert either way, and see what a ferritin result says about your stores.

Your details

Which result?
Units on your report
Result
Anything that changes how it reads?
Sex
Haemoglobin (optional)
TIBC, serum iron only (optional)

For ferritin, the units box does not matter: µg/L and ng/mL are the same number.

18.0 µmol/L is

101 µg/dL

serum iron in the other unit

  • The sumµmol/L x 5.5845 = µg/dL (iron weighs 55.845 g a mole)
  • Micromoles per litre (UK)18.0
  • Micrograms per decilitre (US)101
  • Read forno known inflammation
  • ContextSerum iron swings through the day and after meals, so CKS relies on ferritin rather than serum iron to judge stores.
  • Transferrin saturationadd the TIBC from the same report to work it out
  • Anaemia line for womenhaemoglobin under 120 g/L (WHO); add yours to check

NICE CKS says ferritin is the test that most reliably reflects your iron stores, so check that on your report too. Each lab prints its own serum iron range beside the result.

If a result worries you, ask your GP surgery or practice nurse to talk it through. Call 111 if you feel unwell and are not sure what to do.

The working

Serum iron of 18 µmol/L

Iron weighs 55.845 grams a mole, so 1 µmol/L is 55.845 µg/L, or 5.5845 µg/dL. 18 x 5.5845 = 101 µg/dL. Going back, 101 ÷ 5.5845 = 18.1.

Ferritin

Your iron stores

Ferritin (µg/L)What NICE CKS says
under 15iron stores absent
under 30confirms iron deficiency
31 to 99, no inflammationindeterminate: more tests may be needed
up to 100, with inflammation or CKDcould still be iron deficiency
over 150absolute iron deficiency unlikely even with inflammation
pregnancy, later trimestersfalls by itself; under 15 is depletion, treat under 30

A ferritin of 25 is under 30, so it points to low iron stores; your GP will look for the reason as well as treating it.

Why ferritin

The stores test

NICE CKS says ferritin is the blood test that most reliably reflects your body's iron stores, and it is usually checked alongside a full blood count. Ferritin is harder to read in the second half of pregnancy, when it falls on its own, so your midwife or GP will guide you.

With the rest of your blood test

Haemoglobin and transferrin saturation

Add your haemoglobin to see it against the anaemia line the WHO and the British Society of Gastroenterology use: 130 g/L for men, 120 g/L for women and 110 g/L in pregnancy (your lab may print a slightly different range). Low ferritin with low haemoglobin is the pattern of iron deficiency anaemia; low ferritin with normal haemoglobin means low stores, still worth treating. For serum iron, add the total iron binding capacity (TIBC) from the same report: transferrin saturation is iron ÷ TIBC, so 18 ÷ 70 is 26%. Under 20% points to iron restriction, which helps when inflammation makes ferritin look falsely normal.

Read with care

What this cannot tell you

  • Diagnose anaemiaThat needs haemoglobin from a full blood count.
  • Suggest a doseAsk your GP or pharmacist.
  • Use your lab's rangeRanges vary a little by lab.

Questions

Common questions

How do I convert iron from umol/L to ug/dL?

Multiply by 5.5845. To go back, divide by 5.5845.

What ferritin level is too low?

NICE CKS says a ferritin under 30 micrograms a litre confirms iron deficiency.

Are ng/mL and ug/L the same for ferritin?

Yes, they give exactly the same number.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Talk your results through

If a result worries you, book a chat with your GP or practice nurse, or ask a pharmacist. Call NHS 111 if you feel unwell and are not sure what to do, and 999 in an emergency.

Related

Related calculators