The Ganzoni equation estimates the total amount of elemental iron a patient needs to correct iron deficiency, combining the iron required to rebuild circulating hemoglobin with the iron needed to refill the body's depot stores. It has been the standard basis for dosing intravenous iron since Ganzoni first described it in 1970. This calculator applies that equation and shows how the total splits between its two components.
How the Ganzoni formula works
The formula is total iron deficit (mg) = body weight (kg) x (target hemoglobin - actual hemoglobin, in g/dL) x 2.4 + iron stores (mg). The first term is the hemoglobin-deficit component: the mass of iron needed to raise circulating hemoglobin from the patient's current level up to the target. The added iron-stores term replenishes the body's depot iron on top of that.
The 2.4 constant applies specifically when hemoglobin is measured in g/dL. It combines the iron content of hemoglobin (about 0.34%), blood volume (roughly 7% of body weight), and the unit conversions from g/dL to a total iron mass in mg, working out to approximately 2.4.
Inputs and what they mean
Body weight is in kilograms. Actual hemoglobin is the patient's current level and target hemoglobin is the goal, both in g/dL — the gap between them drives the hemoglobin component. Iron stores is the depot iron to replace, in mg.
By convention, iron stores are about 500 mg for adults and children weighing 35 kg or more, with a target hemoglobin of 15 g/dL. For patients under 35 kg, stores are estimated as roughly 15 mg/kg and the target hemoglobin is usually lowered to 13 g/dL. The stores field defaults to 500 mg and is editable so you can match your local protocol. See the MDCalc Ganzoni page for a reference implementation.
Limits and edge cases
This calculator gives a reference estimate of the total iron deficit — not a prescription. Actual intravenous iron dosing, the choice of product, the number of infusions, and maximum single-dose limits are all product-specific and follow the individual product's prescribing information and your institution's protocols. If a patient's actual hemoglobin already meets or exceeds the target, there is no anemia-based iron deficit and the total reflects only the iron-stores repletion. The equation is an estimate that assumes an average blood volume and hemoglobin iron content, so it should always be interpreted alongside ferritin, transferrin saturation, and the full clinical picture rather than used as a standalone dosing decision.