This page measures a piano; it does not tune one
Play A4 — the A above middle C — and on a piano at concert pitch it reads 440.00 Hz with the needle centred. Middle C reads 261.63 Hz. Those two keys are the whole five-minute check, and they answer the questions an owner actually has: is it still at pitch, how far has it fallen, and how big a job am I about to book?
What this page will not do is talk you through turning the pins. That is a trade — 230 strings at twenty tons of combined tension, a temperament set by ear, and octaves stretched to suit one particular instrument. Reference tones for the whole keyboard are below; use them to find where your piano stands.
Tap a tone to hear the target, then play the matching key and compare on the dial above. The extreme octaves may not reproduce on phone or laptop speakers — use the dial for those, not your ears.
How many keys, and which notes they cover
A full piano is 88 keys running A0 to C8 — 27.50 Hz to 4186.01 Hz. Digital pianos and keyboards cut that down, and they all cut from the same places, so the note range follows directly from the key count:
| Keys | Range | Lowest note | Highest note |
|---|---|---|---|
| 88 | A0 – C8 | 27.50 Hz | 4186.01 Hz |
| 76 | E1 – G7 | 41.20 Hz | 3135.96 Hz |
| 73 | E1 – E7 | 41.20 Hz | 2637.02 Hz |
| 61 | C2 – C7 | 65.41 Hz | 2093.00 Hz |
| 49 | C2 – C6 | 65.41 Hz | 1046.50 Hz |
| 37 | C3 – C6 | 130.81 Hz | 1046.50 Hz |
| 25 | C3 – C5 | 130.81 Hz | 523.25 Hz |
The five-minute pitch check
- Start with A4. Play it firmly and read the dial. This one note tells you most of what you need to know.
- Check middle C, then an octave each way. Play C3, C4 and C5 and write down the cents for each. You are looking for the shape of the drift, not one number.
- Sample the extremes. Something low in the bass, something in the top octave. Do not be alarmed if these read further off than the middle — see below.
- Listen for unisons. Most notes use two or three strings tuned to the same pitch. If the dial hunts and refuses to settle on a note, those strings have drifted apart from each other — which is itself a useful diagnosis.
- Write the numbers down with the date.A history of readings tells a technician far more than “it sounds a bit off”, and it is the difference between a guess and a quote.
| What A4 reads | What it means |
|---|---|
| Within ±5 cents | At concert pitch. A touch-up tuning at most. |
| 5–15 cents flat | Normal drift for a piano a year or so past its last tuning. |
| 15–40 cents flat | Several years untuned. Expect a technician to mention a pitch raise. |
| Around 100 cents flat | A full semitone down — neglected for a long time, and it will need more than one visit to hold pitch. |
| Sharp | Unusual. Often a humidity swing rather than genuine drift; re-check in a week. |
Why a perfectly tuned piano still reads sharp and flat
This is the part that surprises people holding a tuner. Piano strings are stiff, and stiff strings are inharmonic: their overtones sit slightly sharper than exact whole-number multiples of the fundamental. Because we hear an octave by matching one note’s overtones against the note above, a piano octave that sounds right measures slightly wider than a mathematically exact 2:1.
Technicians therefore use stretch tuning: the top octaves progressively sharp, the bass progressively flat, and on a small piano the total can reach 30 cents at the extremes. So a top octave reading sharp and a bottom octave flat while the middle sits at zero is not a fault — it is a well-tuned piano, and forcing every note to zero would make it sound worse. Our guide to cents covers the measurement side.
Frequently asked questions
What are the frequencies of piano keys?
An 88-key piano runs from A0 at 27.50 Hz to C8 at 4186.01 Hz, and every key between follows f = 440 × 2^((n − 69)/12) on its MIDI number. The landmarks worth memorising are A4 at 440.00 Hz (concert pitch), middle C4 at 261.63 Hz, and the C either side at 130.81 and 523.25 Hz. Tap any tone in the reference panel above to hear it. One caveat: those are equal-temperament values, and a correctly tuned piano deliberately sits a little off them at the extremes — see stretch tuning above.
How many keys does a piano have, and what notes do they cover?
A full-size piano has 88 keys covering A0 to C8. Keyboards cut that down from the same places: 76 keys is E1–G7, 73 is E1–E7, 61 is C2–C7, 49 is C2–C6, 37 is C3–C6 and 25 is C3–C5. Note that Yamaha labels middle C as C3 rather than C4, so a Yamaha 61-key board covers what this page calls C2–C7 but its own panel calls C1–C6. The pitches are identical either way.
What frequency is middle C on a piano?
Middle C — C4, the C nearest the middle of the keyboard — is 261.63 Hz in equal temperament with A4 at 440 Hz. On a real piano the measured value will sit a few cents either side of that because of stretch tuning, and that is correct rather than wrong. Tap the highlighted C4 in the reference tones above to hear it.
Can I tune my own piano with this?
Honestly, no — not to a good result. Beyond the tuning lever and mutes you would need, the skill is in setting a temperament by ear and stretching the octaves to suit that particular instrument, and neither is something a chromatic dial can guide you through. What you can do is measure precisely where your piano stands, which is genuinely worth knowing before you call anyone. Instruments where DIY tuning is realistic include the guitar, the kalimba and, with care, the accordion.
How often does a piano need tuning?
Once or twice a year for a piano in a home, and considerably more often for one being recorded or performed on. New pianos need more attention in their first couple of years while the strings and frame settle. The real driver is humidity stability, not how much you play — an untouched piano in a room with swinging humidity will drift faster than a well-housed one played daily.
Why won't the tuner settle on a note?
Almost always because that note’s two or three strings have drifted apart from each other. The tuner hears several close pitches at once and hunts between them. It is a reliable way to find which notes have unison problems — play up the keyboard and note every key where the dial refuses to lock. Sustain pedal down and other notes still ringing will cause the same symptom, so check with everything else damped.