Iron Deficit Calculator
Ganzoni iron need from weight and Hb gap.
What it does
Iron deficit estimates how much iron repletion must replace to normalize hemoglobin and refill stores. Anemia care uses it to pick IV iron totals, because pills alone cannot close large gaps on time. The Ganzoni method links weight, hemoglobin gap, and a stores allowance in one line.
The tool above runs that line. At 70 kg with Hb 9 to 15, the gap is 6 and the deficit is 1,508 mg with 500 mg of stores. The imperial mirror at 154 lb gives 1,506 mg, the small gap coming from pound rounding. Both modes convert to kilograms inside, so the physiology stays in one unit.
The 2.4 factor packs three facts: blood near 7% of body weight, hemoglobin iron near 0.34%, and the change from grams per deciliter to milligrams. Stores add 500 mg at adult weights and 15 mg per kg below 35 kg. Targets vary by protocol, with 15 classic for adults and lower values for children and pregnancy.
This page estimates for discussion with clinicians. It does not prescribe, split infusions, or clear safety checks such as allergy history and transferrin saturation. Estimates for information only, not medical advice.
How to use
- Pick metric (kg) or imperial (lb).
- Enter body weight.
- Enter current hemoglobin in g per dL.
- Enter the protocol target hemoglobin.
- Read total deficit first, then gap and stores.
- Confirm dose and splits with the care team.
Formula
- weight
- Body weight in kg, converted from lb when imperial is picked.
- gap
- Hemoglobin gap in g per dL, target minus actual, above zero.
- stores
- 500 mg at 35 kg and up, else 15 mg per kg.
Ganzoni method for total body deficit to guide repletion. At target at or below actual there is no deficit to compute. Weight converts from lb at 0.45359237 when imperial is picked.
Worked example
Example: 70 kg, Hb 9 to 15
Defaults: metric 70 kg with Hb 9 to 15. Imperial mirror is 154 lb. Target above current is required.
- Inputs (metric default): 70 kg, current Hb 9, target 15 g per dL.
- Gap: 15 minus 9 is 6 g per dL gap.
- Stores: weight above 35 kg gives 500 mg stores.
- Deficit: 70 times 6 times 2.4 plus 500 is 1,508 mg deficit.
- Imperial mirror (154 lb, same Hb) gives 1,506 mg deficit. Tool shows the same three outputs.
Reference table
| Case | Math | Deficit |
|---|---|---|
| 70 kg, 9 to 15 | 70x6x2.4+500 | 1,508 mg deficit |
| 60 kg, 10 to 14 | 60x4x2.4+500 | 1,076 mg deficit |
| 80 kg, 11 to 15 | 80x4x2.4+500 | 1,268 mg deficit |
| 154 lb, 9 to 15 | 69.9x6x2.4+500 | 1,506 mg deficit |
| 50 kg, 11 to 15 | 50x4x2.4+500 | 980 mg deficit |
Limits
- Estimate only. Product labels and protocols rule dosing.
- Adult 15 target is classic, not universal. Use protocol target.
- No safety screen. History and labs decide fitness for infusion.
- Ongoing bleeding invalidates one static total.
Common mistakes
- Entering hemoglobin in g per L instead of g per dL, off by ten.
- Using lb as kg, which more than doubles the answer.
- Skipping stores and underdosing by 500 mg.
- Self dosing IV iron from a web number.
- Treating one total as final with active losses.
Try it yourself
Quick checks. Answers sit tucked under each question.
60 kg, Hb 10 to 14?
Gap is 4. Deficit is 60 times 4 times 2.4 plus 500 is 1,076 mg deficit.
80 kg, Hb 11 to 15?
Gap is 4. Deficit is 80 times 4 times 2.4 plus 500 is 1,268 mg deficit.
Questions
How is iron deficit figured?
Deficit = weight times gap times 2.4 plus stores. Here 70 times 6 times 2.4 plus 500 is 1,508 mg deficit.
Where does 2.4 come from?
2.4 folds blood volume near 7% of weight with hemoglobin iron near 0.34%, plus unit changes from g per dL to mg.
How are iron stores set?
500 mg at 35 kg and above, else 15 mg per kg. Here 500 mg stores.
Can I use this for pills at home?
No. This guides IV iron dosing with the care team. Do not self dose iron from this number.
Does pregnancy use 15?
Yes. Pregnancy often uses 11 to 12 targets by protocol. Enter the protocol target to recompute.
When do I recheck?
Reassess in about 4 weeks with labs. Ongoing losses need repeat dosing, not one static number.