Iron Deficiency Calculator — Ganzoni Formula
Estimate the total iron deficit in mg using the Ganzoni formula (1970): body weight (kg) × (target Hb − actual Hb g/dL) × 2.4 + iron stores. Used clinically to guide intravenous iron replacement in iron-deficiency anaemia.
kg
Sex
g/dL
g/dL
Ganzoni formula: weight × (target Hb − actual Hb) × 2.4 + iron stores
- 1
Iron for Hb correction
70 × (13 − 9) × 2.4 = 672 mgFactor 2.4 converts the Hb deficit per kg of body weight to milligrams of elemental iron. - 2
Iron stores to replenish
500 = 500 mgFixed 500 mg for adults ≥ 35 kg. - 3
Total iron deficit
672 + 500 = 1,172
How does this calculator work?
The Ganzoni formula estimates total iron deficit as: body weight (kg) × (target Hb − actual Hb g/dL) × 2.4 + iron stores (500 mg for adults ≥ 35 kg). Enter weight, sex, actual Hb and target Hb. A 70 kg adult with Hb 9 g/dL targeting 13 g/dL needs approximately 1172 mg of elemental iron. For clinical use only.
Formula
How this is calculated
The Ganzoni formula (1970) estimates the total body iron deficit in two parts. The first part — weight × (target Hb − actual Hb) × 2.4 — corrects for the haemoglobin deficit. The factor 2.4 derives from the iron content of haemoglobin: blood volume is approximately 70 mL/kg, haemoglobin is about 10 g/L per g/dL, and haemoglobin contains 3.4 mg of iron per gram, so 0.07 L/kg × 10 g per g/dL × 3.4 mg/g ≈ 2.4 mg/kg per g/dL of Hb deficit.
The second part adds iron stores to replenish the body's non-haemoglobin iron reserves: 500 mg for adults weighing 35 kg or more, or 15 × body weight in kg for lighter patients. These store values are clinical estimates from the original Ganzoni paper and remain the widely-used standard despite being approximations.
The target haemoglobin is typically 13 g/dL for adults of both sexes, though some guidelines use 15 g/dL for males or adjust for the indication. WHO defines anaemia as Hb < 13 g/dL in men and < 12 g/dL in non-pregnant women (2011). The formula gives a total iron deficit in milligrams — the route and formulation of iron replacement (oral, IV ferric carboxymaltose, iron sucrose, etc.) are decided by the treating clinician. This calculator is an estimation aid only.
Frequently asked questions
The factor 2.4 converts a haemoglobin deficit (in g/dL) per kg of body weight into milligrams of elemental iron. It comes from: blood volume ≈ 70 mL/kg × conversion factor 10 g/L per g/dL × iron content of Hb 3.4 mg/g ≈ 2.38, rounded to 2.4. It accounts for the fact that increasing Hb by 1 g/dL across the whole blood volume requires roughly 2.4 mg of iron per kg of body weight.
The body stores iron in ferritin and haemosiderin in the liver, spleen, and bone marrow. Depleted iron stores must be refilled after correcting haemoglobin, or anaemia will recur. The Ganzoni formula uses a fixed 500 mg for adults ≥ 35 kg (an average estimate) and 15 × weight kg for smaller patients. Actual stores vary widely; a serum ferritin < 15 µg/L confirms depletion.
The target Hb is the level you aim to restore the patient to. Common choices are 13 g/dL (lower end of normal for adults of both sexes, WHO 2011), 14–15 g/dL (mid-normal for men), or the pre-illness Hb if known. Your clinical team will specify the appropriate target for the patient's condition and tolerance of anaemia.
Also known as
TG we-Calculate Editorial Team. (2026). Iron Deficiency Calculator — Ganzoni Formula [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/iron-deficiency-calculator
TG we-Calculate Editorial Team. "Iron Deficiency Calculator — Ganzoni Formula." TG we-Calculate. 2026. https://we-calculate.com/calculator/iron-deficiency-calculator.
TG we-Calculate Editorial Team, "Iron Deficiency Calculator — Ganzoni Formula," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/iron-deficiency-calculator
@misc{wecalculate_iron_deficiency_calculator, title = {Iron Deficiency Calculator — Ganzoni Formula}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/iron-deficiency-calculator}}, year = {2026}, note = {TG we-Calculate} }
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