Un Norwood 3 suele necesitar 1.500–1.900 injertos; un Norwood 5, unos 3.700–4.700. La cifra depende del área despoblada, la densidad objetivo y lo que la zona donante puede ceder con seguridad; aquí se ve todo el cálculo.
La caída sigue un patrón distinto en hombres y mujeres, por eso se usa otra escala.
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Most graft calculators print a range and never say where it came from. This one is arithmetic you can check: the area to be covered, multiplied by the density you are aiming for, adjusted for how thick your hair is — then capped by what your donor area can actually spare over a lifetime.
grafts = recipient area (cm²) × target density (FU/cm²) × caliber factorEach Norwood or Ludwig stage corresponds to an area of scalp that needs covering. These are the planning areas in general clinical use, and they are the reason a graft estimate given without a stage is a guess. Norwood 2 is a small frontal correction; Norwood 7 is most of the top of the head.
| Stage | Area | Stage | Area |
|---|---|---|---|
| Norwood 2 | 20 cm² | Norwood 5 | 110 cm² |
| Norwood 3 | 45 cm² | Norwood 6 | 145 cm² |
| Norwood 3V | 65 cm² | Norwood 7 | 190 cm² |
| Norwood 4 | 80 cm² | Ludwig 2 | 90 cm² |
Native hair sits at roughly 80–100 follicular units per cm². A transplant does not reach that. Exceeding about half of native density in a single session risks the survival of the grafts, which is why promises above 45 FU/cm² should be treated with suspicion. This tool offers 30 FU/cm² for coverage-focused, donor-sparing planning, 38 as the common target, and 45 as an upper bound that is not achievable for everyone.
The safe donor zone — the occipital and parietal areas that androgenetic loss does not affect — is roughly 120 cm². Taking more than about 25% of its existing density causes visible, permanent thinning of the donor itself. At a measured density of 60 FU/cm² for a weak donor and 95 for a strong one, an average donor yields around 2400 grafts over a lifetime, across all sessions. That figure is a ceiling, not a target.
This is the part most calculators leave out entirely, and it is the most common planning failure in the industry. A 25-year-old at Norwood 3 whose loss is still progressing will not stay at Norwood 3. If the whole donor is spent now, there is nothing left when he reaches Norwood 5 at 40 — and he is left with a hairline that does not match his age. The tool holds back a share of the donor accordingly, from 40% under 25 down to nothing past 45 once loss has settled.
Thicker hair produces the same visual coverage with fewer follicles. Fine hair needs about 1.15× the grafts for the same result; thick hair needs about 0.85×. This is a real effect and not a rounding factor — it can shift an estimate by several hundred grafts.
These are planning ranges, not measurements. A real graft count is determined at a physical examination: donor density measured by trichoscopy, your actual recipient area, hair-to-skin colour contrast, curl, scalp laxity and your medical history. Any clinic that quotes a firm number from a photograph, without measuring anything, is selling rather than assessing. Use this to sanity-check what you are told, not to replace it.