Ganzoni Iron Deficit Calculator (IV Iron Dose)
Total iron deficit by the Ganzoni formula — weight × (target − actual haemoglobin) × 2.4 + iron stores — in g/dL, g/L or mmol/L, with actual or ideal body weight, the Ferinject and Monofer simplified-table doses and an infusion plan split by the chosen product’s maximum single dose.
How it works
Iron deficit (mg) = weight (kg) × (target Hb − actual Hb) (g/dL) × 2.4 + iron stores (500 mg; 15 mg/kg below 35 kg) · ideal weight = 25 × height (m)² · Hb g/dL = g/L ÷ 10 = mmol/L × 1.611 · doses = course ÷ maximum single dose, rounded up
Ganzoni’s 1970 formula converts a haemoglobin shortfall into milligrams of iron. Each gram of haemoglobin contains 3.4 mg of iron, and blood volume is roughly 70 mL/kg, which gives the constant 2.4 (3.4 × 0.07 × 10 for the unit change from g/dL); a further 500 mg is added so that the patient finishes with replenished stores, not just a corrected haemoglobin. Below 35 kg the product labels use 15 mg/kg for stores and a target of 13 g/dL. Haemoglobin can be entered in g/dL, g/L or mmol/L, and weight in kg or lb. Because blood volume does not rise in proportion to fat, the Monofer label advises using ideal weight (BMI 25 × height²) in obesity, and pre-pregnancy weight in pregnancy. Modern IV iron products also come with simplified weight-and-haemoglobin tables, which often give more iron than Ganzoni; both the Ferinject and Monofer tables are shown. Choose a product to split the course into doses no larger than its maximum single dose (for example 20 mg/kg up to 1,000 mg of ferric carboxymaltose a week, or 200 mg of iron sucrose) and to see the volume of each dose. Ferritin and transferrin saturation are rechecked about four weeks after the last dose.
Worked example
70 kg, haemoglobin 9 g/dL, target 13, stores 500 mg: 70 × 4 × 2.4 = 672 + 500 = 1,172 mg — about 1,200 mg, given as ferric carboxymaltose 1,000 mg (20 mL) then 200 mg (4 mL) at least a week later. The Ferinject table for Hb under 10 g/dL and 70 kg or more would give 2,000 mg. With the label target of 15 g/dL the Ganzoni deficit is 70 × 6 × 2.4 + 500 = 1,508 mg, which matches the 75 mL of iron sucrose (1,500 mg) in the Venofer dosing table, given as eight doses of up to 200 mg.
Sources: Ferinject (ferric carboxymaltose) — Summary of Product Characteristics, section 4.2 (emc) · Monofer (ferric derisomaltose) — Summary of Product Characteristics, section 4.2 (emc) · Venofer (iron sucrose) — Summary of Product Characteristics, section 4.2 (emc) · NIH/NLM DailyMed — US labels for Injectafer, Monoferric, Venofer, Ferrlecit, Feraheme and INFeD
Frequently asked questions
Why do the dosing tables give more?
Studies showed Ganzoni under-doses many patients, particularly those with ongoing losses; the FERGIcor trial found the simplified regimen (1,500–2,000 mg) more effective for IBD patients.
How fast will haemoglobin rise?
Expect about 1–2 g/dL within two to four weeks after adequate IV iron, faster than with oral iron, with a reticulocyte response in 5–10 days.
Which weight should I use?
Product labels use actual body weight, with pre-pregnancy weight in pregnancy. In obesity, actual weight overstates blood volume, so the Monofer label suggests ideal weight (BMI 25 × height²). Choose “Lower of actual and ideal” to apply that only when it gives a smaller weight.
What target haemoglobin should I enter?
The Venofer and Monofer labels use 15 g/dL (13 g/dL below 35 kg). Many clinicians use 12–13 g/dL, closer to the lower limit of normal. The table under the results shows the deficit for targets from 12 to 15 g/dL.
How is the course split into infusions?
Each product has a maximum single dose: ferric carboxymaltose 20 mg/kg up to 1,000 mg (15 mg/kg up to 750 mg in children), ferric derisomaltose 20 mg/kg (capped here at 1,000 mg), iron sucrose 200 mg, ferric gluconate 125 mg, ferumoxytol 510 mg and iron dextran 100 mg a day. The plan fills each dose up to that limit, with the remainder in the last one.
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Clinical decision tool for education and for use by trained clinicians alongside judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.