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RO Punch diameter in follicular unit excision typically runs from 0.7 mm to 1.1 mm. The working rule is to use the smallest punch that still encloses the follicular unit without cutting into it.
What sets that number is measurable anatomy rather than preference:
| What is measured | Why it moves the diameter |
|---|---|
| Hairs per follicular unit | More hairs need a wider circle to be enclosed intact |
| How far the hairs splay below the skin | Wide splay demands a larger punch than the surface suggests |
| Hair shaft calibre | Coarse shafts fill more of the punch lumen |
| Donor skin firmness | Firm skin resists the punch and shifts the safe margin |
The tip geometry matters as much as the number. When punch types were compared at a single fixed diameter, the blunt punch produced the least follicular damage and the best graft-to-hair ratio, while the sharp punch transected most (Mohmand & Ahmad, Journal of Cosmetic Dermatology, 2019). Two clinics quoting the same diameter are not necessarily doing the same thing.
A smaller punch is not automatically a mark of a better clinic. Below the diameter the anatomy allows, transection rises and the grafts that arrive are damaged. The scar is smaller and the yield is worse.
In the donor plan, diameter decides how much skin each extraction removes. That is what limits how many grafts a donor area can give across a lifetime, not how many can be taken in one session.
Related terms
- Safe donor area
- Donor overharvesting
- Graft extraction angle
- FUE extraction science
- Hair follicle anatomy
For how extraction is performed and what governs graft survival, see the FUE technique. For how much the donor area can safely give, see the donor area.
