What gets measured, exactly

The measurement

Two open models run on your device: MediaPipe's face landmarker (478 facial points) and its hair segmenter (a per-pixel hair-probability map). From the landmarks we anchor five vertical scan columns to your brows — centre, both brow peaks, both brow outer ends, because the frontotemporal angle the Norwood scale cares about sits above the brow's outer end. Each column walks upward from just above the brow until it meets a solid run of hair; that meeting point's height, in brow-to-chin units, is your hairline profile.

The staging signal is recession: average temple-column height minus centre-column height. Below 0.08 face-units reads as stage 1, up to 0.18 as stage 2, up to 0.35 as stage 3, beyond that as deep frontal loss — with a centre hairline above 0.72 face-units bumping the read one stage, since a uniformly high line under-reports on temple recession alone. Within 0.03 face-units of any cut-off the verdict is presented as borderline, with the neighbouring stage named.

These thresholds derive from standard facial-proportion anatomy (a non-recessed hairline sits about half a brow-to-chin unit above the brow; the stage cut-offs correspond to roughly one and two-plus centimetres of temple recession on an average head). We validate and tune them against photographed, staged examples as they accumulate; when a threshold changes, this page changes with it, dated.

A front-facing photo contains no crown. Rather than pretend otherwise, the tool stages the front from measurement and asks you two questions about the rest: the state of your crown, and — when it separates stages — whether a band of hair still divides front from crown. Those answers route the verdict through the same table a clinician's intake questions would.

• No face found — nothing is staged from a photo without one.
• Head turned or tilted too far — beyond ±14° of turn or ±15° of tilt the temple columns drift off the frontotemporal angles, so the tool asks for a straight-on shot instead of mismeasuring.
• No readable frontal hair — a hat, a headband, very light or shaved hair and an already-bare top all look identical to a segmenter (under 10% hair coverage in the zone where frontal hair sits). The tool switches to questions rather than guess which one it saw — reading a hat as a Norwood 6 is this tool's worst possible failure, so it is the one most explicitly designed out.

The Norwood scale itself is a shorthand — real heads sit between stages and off the chart's idealised patterns, which is why borderline verdicts name both stages. Segmentation quality drops on very light hair against light skin and in harsh backlight; the refusal rules catch most of this, not all. And a stage is a position, not a trajectory — the tool cannot tell a stable hairline from a moving one, which is why the maturing-or-receding guide leans on year-apart photos. None of this is medical diagnosis, and sudden or patchy loss belongs with a doctor, not a scale.