TIBC from Transferrin Calculator

Estimate total iron binding capacity from a measured transferrin concentration when your laboratory reports one but not the other.

Last updated 31 Aug 2026

TIBC from Transferrin

Transferrin → TIBC

Transferrin (mg/dL)Multiply g/L by 100 first.

331µg/dLExample

Transferrin 265 mg/dL (2.65 g/L)

Formula

TIBC (µg/dL) ≈ Transferrin (mg/dL) × 1.25

1.25: each transferrin molecule binds two ferric ions; the factor converts protein mass to iron-binding capacity
g/L: multiply by 100 to obtain mg/dL before applying the factor

Worked example

Transferrin 265 mg/dL (2.65 g/L)
265 × 1.25 = 331 µg/dL
= 59.3 µmol/L

Equivalent values

The 1.25 factor is an approximation. Where both are measured on the same sample the values usually agree within about 10%.
Transferrin mg/dL	Transferrin g/L	Estimated TIBC µg/dL
200	2.00	250
265	2.65	331
300	3.00	375
360	3.60	450

When to use the estimate

Laboratories measure iron-binding capacity in one of two ways. Some assay transferrin directly by immunoturbidimetry and report a protein concentration; others measure the capacity functionally, saturating the sample with iron and reporting TIBC. Clinicians and guidelines are written in terms of both, so converting between them is a routine need.

The factor of 1.25 comes from stoichiometry: each transferrin molecule carries two ferric ions, so a known mass of transferrin corresponds to a calculable mass of bindable iron. The conversion is close but not exact, because a small proportion of iron-binding capacity in plasma is not transferrin, and because the immunochemical and functional assays are standardised differently.

Treat the result as an estimate suitable for interpreting a reference range or calculating an approximate transferrin saturation. Where a precise saturation matters — screening for haemochromatosis, for instance — measure iron and TIBC on the same sample rather than deriving one from the other.

Frequently asked questions

Why is the conversion factor 1.25?

Each transferrin molecule binds two ferric ions. Working from the molecular weight of transferrin and the atomic weight of iron gives roughly 1.25 µg of bindable iron per mg of transferrin per decilitre.

My transferrin is reported in g/L — what do I do?

Multiply by 100 to get mg/dL, then apply the factor. A transferrin of 2.65 g/L is 265 mg/dL, giving an estimated TIBC of 331 µg/dL.

Is the estimate good enough to calculate transferrin saturation?

For routine interpretation, yes. For haemochromatosis screening, where the 45% threshold matters, measure serum iron and TIBC on the same sample instead.

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References

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, transferrin and iron-binding capacity.
Gottschalk R et al. Comparison of directly measured transferrin with calculated TIBC. Clin Chem.

Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.