Inharmonicity Meter
Piano strings are stiff, so their partials sit sharp of true harmonics. Play a single note and this measures how sharp, and fits the inharmonicity coefficient B for that string.
Press the button, then strike one note firmly and let it ring. It waits for the strike, so take your time. Everything is measured in your browser and no audio is recorded or sent anywhere.
What the number means
B is the coefficient in f(n) = n·f₁·√(1 + Bn²), which places the nth partial above a true harmonic. It runs around 3 to 5 ×10⁻⁴ through the midrange of a decent grand and climbs by an order of magnitude into the top octave. Shorter strings mean more inharmonicity, which is why small pianos stretch harder than concert grands.
Deviations here are referenced to the note’s own sounding first partial. Robert Young’s 1952 paper references the ideal stiffness-free string instead, and the two conventions differ by four thirds at the second partial, so check which one a table is using before comparing figures.
What it can’t do
This is a browser and a microphone, not a calibrated instrument. It was validated against synthesised tones of known B, where it recovers the value to within a few percent across the compass. Synthetic audio is the easy case. A real room adds reverberation, sympathetic ringing from undamped strings, false beats, and whatever your microphone does to the top octave.
When the partials don’t fit a stiff-string model closely, the tool shows no number instead of a bad one. If you get a refusal, the usual causes are a second note still sounding, a strike that has already decayed, or background noise.
The bass is the hardest region. Wound strings carry their stiffness in the core and their mass in the winding, so B stops being predictable from the finished string, though the measurement itself still describes what the string is doing.
For why this number moves after a pitch raise, and how much of it matters, see Should you remeasure inharmonicity after a pitch raise?