Iron Deficit (Ganzoni) Calculator
Enter weight, current Hb and target Hb to get the total iron deficit.
Result
How it is calculated
The tool adds a haemoglobin-based part to a fixed allowance for iron stores: deficit (mg) = weight × (target Hb − current Hb) × 2.4 + 500. Weight is in kg, both haemoglobin values are in g/dL, and the factor 2.4 converts the haemoglobin gap per kilogram into milligrams of iron. The stores part is always 500 mg here, whatever the body weight, so the figure is a ready-made adult value and is not lowered for small patients. The result lists the total, the haemoglobin part and the stores. The target must be higher than the current value. Weight must be 2 to 650 kg, current haemoglobin 1 to 30 and target no more than 30 g/dL; anything outside these limits shows no result. This is a planning figure for clinical use; the dose is decided by the treating clinician, not by this page.
Worked example
A patient weighs 65 kg, has a haemoglobin of 9.5 g/dL, and the target is 13 g/dL. The gap is 13 − 9.5 = 3.5 g/dL. Haemoglobin part = 65 × 3.5 × 2.4 = 546 mg. Adding the 500 mg stores gives a total iron deficit of 1,046.00 mg. If the target were lowered to 12 g/dL, the gap would be 2.5, the haemoglobin part 390 mg and the total 890 mg.
Common mistakes
- Entering haemoglobin in g/L (95 and 130) instead of g/dL (9.5 and 13). Values above 30 are rejected, so the tool shows no result rather than a deficit ten times too large; retype the values in g/dL.
- Swapping the current and target values; the tool then gives no result because the target must be above the current value.
- Using the formula for a child or a very small adult without noticing that the stores allowance is fixed at 500 mg here.
- Entering a haemoglobin target taken from a normal range for the wrong sex or situation, which changes the gap and the dose.
- Treating the total as the single infusion dose: the figure is the cumulative deficit, and how it is split across doses is for the clinician to decide.
About this calculator
The Ganzoni formula, published in 1970, calculates the total body iron deficit that needs to be replaced (typically via IV iron infusion) in patients with iron-deficiency anemia: Total iron deficit (mg) = weight (kg) × (target Hb − current Hb) (g/dL) × 2.4 + iron stores (mg), where the 2.4 factor converts the hemoglobin gap into the iron mass needed to close it, and iron stores are conventionally assumed to be 500 mg for adults over 35 kg (lower for smaller patients). This calculator always adds the fixed 500 mg, so for a patient under 35 kg its total runs higher than a size-adjusted figure; it also shows the weight and hemoglobin part and the stores part separately.
Hematologists and gastroenterologists use this formula to dose IV iron precisely for patients who can't tolerate or don't respond adequately to oral iron — chronic kidney disease, inflammatory bowel disease and heavy menstrual bleeding are common reasons — since giving too little iron leaves the anemia under-treated while overshooting risks iron overload, so the formula-driven dose matters more here than a rough estimate would in most other supplement dosing.
This calculator takes body weight, current hemoglobin and target hemoglobin and returns the total iron deficit in milligrams using the Ganzoni formula.
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