What is the Iron Deficiency Calculator?
This calculator estimates the total amount of elemental iron (in milligrams) a person needs to correct iron deficiency anemia. It uses the well-known Ganzoni formula, widely applied in clinical practice to dose intravenous iron replacement. It is an educational estimate only — actual dosing decisions must be made by a qualified clinician.
How to use it
Enter the patient's body weight in kilograms, the current (actual) hemoglobin, the desired target hemoglobin, and the iron stores value. For adults the iron stores depot is conventionally taken as 500 mg (for body weight under 35 kg, 15 mg/kg is often used instead). The calculator returns the total iron deficit to be replaced.
The formula explained
The Ganzoni equation is:
$$\text{Iron deficit (mg)} = \text{body weight (kg)} \times \left( \text{target Hb} - \text{actual Hb} \right) \times 2.4 + \text{iron stores (mg)}$$
The constant 2.4 combines two factors: blood volume is roughly 7% of body weight (0.07 L/kg), and 1 g of hemoglobin contains about 3.4 mg of iron, giving \(0.07 \times 3.4 \times 10 = 2.4\) when Hb is in g/dL. The iron stores term replenishes the body's depot iron once circulating hemoglobin is restored.
Worked example
For a 70 kg adult with actual Hb of 9 g/dL, a target of 15 g/dL, and 500 mg iron stores: $$70 \times (15 - 9) \times 2.4 + 500 = 70 \times 6 \times 2.4 + 500 = 1008 + 500 = \mathbf{1508}\ \textbf{mg}$$ of iron to replace.
FAQ
Why use 500 mg for iron stores? 500 mg represents typical depleted-but-not-zero depot iron reserves to be replenished in adults over 35 kg. Lighter patients use 15 mg/kg.
What target hemoglobin should I use? A target of 15 g/dL is common for adults, but the clinically appropriate target varies by sex, age, and condition.
Is this the dose to give in one infusion? No. The total deficit is often divided across multiple doses depending on the iron product's maximum single dose and the patient's tolerance.
