Health
Ferritin Calculator — Iron Status Thresholds for Athletes
Read your ferritin result against the thresholds used for endurance athletes, which sit higher than standard reference ranges, with checks for inflammation and anaemia.
The two units are numerically identical.
Only used for the haemoglobin cut-off.
mg/L. Checks whether the reading is inflated.
g/dL. Separates deficiency from anaemia.
Below the 30 mark commonly used to flag iron deficiency. Many general-population reference ranges would call this normal, which is why athletes are often told their bloods are fine.
This tool reads a number you already have against thresholds used in athlete populations — it is education, not a diagnosis, and it cannot tell you why your stores are low. Do not start iron supplementation on the basis of a calculator: excess iron is harmful, and the underlying cause matters more than the number. Ferritin also shifts with recent training, so results drawn within a day or two of a hard session are less reliable.
Why athlete thresholds are higher
Most laboratory reference ranges are built from the general population, where ferritin below roughly 15 ug/L flags deficiency. Endurance athletes are routinely told their bloods are "normal" on that basis while sitting at a level that affects training.
The athlete literature uses higher cut-offs. Deficiency is commonly flagged below 30 ug/L, with severity steps at 20 and 10, and the 30 to 50 band is widely described as suboptimal — hepcidin elevations are reported in that range. Some authors argue for 40 to 50 as the working threshold in endurance populations.
Serum ferritin in ug/L and ng/mL are numerically identical, so a result in either unit reads the same here.
Ferritin alone is not enough, for two reasons
It rises with inflammation. Ferritin is an acute-phase reactant. Infection, injury, illness and recent hard training push it up regardless of iron stores, so a reassuring number can sit on top of a genuine deficiency. This is why CRP is usually run alongside it, and why a result drawn a day after a long run is less useful than one taken rested.
It cannot tell you whether you are anaemic. Low ferritin with normal haemoglobin is iron deficiency without anaemia, which still affects training capacity. Low ferritin with low haemoglobin is iron deficiency anaemia. The WHO haemoglobin cut-offs are 13.0 g/dL for men and 12.0 g/dL for non-pregnant women. Add your haemoglobin above and the tool will tell you which side of that line you are on.
Why endurance athletes lose iron
Losses run higher than in sedentary people through several routes at once: foot-strike haemolysis, sweat, gastrointestinal losses during hard efforts, and in menstruating athletes, monthly blood loss. Exercise-induced hepcidin also suppresses absorption for several hours after hard sessions, which is why supplement timing matters when it is warranted.
Chronically low energy availability makes all of this worse, since intake is the other side of the ledger — the energy availability calculator covers that side.
What this tool will not do
It will not diagnose you, and it will not tell you to take iron. Supplementing without knowing why stores are low can mask a cause that matters, and excess iron is harmful — this is not a nutrient where more is better. Treat the output as a way of understanding a number you already have, then take it to whoever ordered the test.
Frequently Asked Questions
What ferritin level is too low for a runner?
Below 30 ug/L is the level most commonly used to flag iron deficiency in athletes, with 20 and 10 marking progressively more depleted stores. Between 30 and 50 is often described as suboptimal for endurance athletes rather than deficient. These sit above typical laboratory reference ranges, which is why an athlete can be told their result is normal while still being low for their training load.
Are ug/L and ng/mL different?
No. For serum ferritin the two units are numerically identical, so a result of 28 ug/L and 28 ng/mL are the same value. Laboratories in different countries report one or the other, and no conversion is needed.
Can a normal ferritin still mean I am iron deficient?
Yes. Ferritin is an acute-phase reactant, so infection, injury, illness or a recent hard training session raise it independently of how much iron you have stored. A value that looks adequate can sit on top of a real deficiency. CRP is usually measured alongside ferritin for this reason, and a result drawn when you are healthy and rested is more informative than one taken shortly after a hard effort.
What is the difference between iron deficiency and iron deficiency anaemia?
Iron deficiency without anaemia means stores are depleted while haemoglobin is still within range — training adaptation and perceived effort can already be affected at this stage. Iron deficiency anaemia means haemoglobin has fallen below the WHO cut-off as well, 13.0 g/dL in men and 12.0 g/dL in non-pregnant women. Ferritin alone cannot distinguish the two, which is why haemoglobin is an input here.
Should I start taking iron if my ferritin is low?
Not on the basis of a calculator. Iron supplementation should follow a conversation with a clinician, because the dose, the form, the timing and the duration all matter, and because the reason stores are low can be more important than the number itself. Excess iron is harmful, and supplementing blindly can also mask a cause that needs investigating.
When should I get my blood drawn?
When you are healthy, not recovering from illness or injury, and not within a day or two of a hard or long session. Both ferritin and CRP respond to recent training, so a sample taken in a normal rested state gives a number that is easier to interpret and easier to compare against a future test.
Data sources & references
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