Piano Tuner Online
This piano tuner online runs in the browser on your phone or computer, free and with nothing to install. Pick a key on an 88-key keyboard, from A0 (27.5 Hz) to C8 (4,186 Hz), or let the tool recognize which key you played: the screen shows the note, the frequency in Hz, how many cents the sound is above or below the target, and a needle that holds still when the reading is steady. In the bass, where the fundamental barely reaches the microphone, the pitch is worked out from the partials of the string. There is also a unison mode, a step-by-step guide and a colored map of the keys you have measured, saved only on your device.
How to use it
- Tap Turn on microphone, allow access and place the device near the strings or the open lid, away from fans and conversation.
- In Recognize the key mode, play a key and let it ring: the note, the frequency and the cents appear. To check a specific key, tap it on the on-screen keyboard (or use the arrow buttons) and the mode switches to Chosen key.
- Read the needle a second or two after the attack. Green means within ±3 cents of the target; amber, within ±8; red, more than that. Every key measured with a steady reading takes that color on the keyboard and on the map.
- Follow the step-by-step guide: the Next in guide button jumps to the next key that is not green yet, starting at A4.
- To match the strings of one key, turn on Unison, play the key and watch the beating. Under Settings you can change the reference A and the note names and see the stretch curve.
Help and explanations
The tool measures and guides; it does not replace a professional piano tuner. Real tuning takes a tuning hammer, the skill to set a pin without straining the pinblock, and ear training. Use it to find out where your piano stands, to follow a technician's work or to study tuning with a teacher. A digital piano never goes out of tune: see the question at the end of the page.
Where to start: A440, the temperament octave and octaves
Tuning starts from a reference: A4 at 440 Hz, the A just to the right of middle C. With the other strings of that key muted, the first A4 string is set to a tuning fork or a tuner. Next comes the temperament octave, F3 to F4, where the 12 notes of the middle octave are set one by one; it defines the equal temperament of the whole piano.
With the middle done, a tuner works up in octaves to C8 and down to A0, comparing each new note with the octave already tuned. Last come the unisons: most keys have two or three strings that must sound as one. The map stays saved in this browser; the Start over button clears it for a new round.
Bass, treble and the stretch curve
Piano strings are stiff steel, so the partials of a note come out slightly sharper than exact multiples of the fundamental: this is inharmonicity. In the bass, the fundamental also hardly sounds, even less on an upright or through a phone microphone. The tool then uses partials 2, 3, 4 and up, works out the inharmonicity of that very string and still shows the reading of the fundamental, telling you which partials it used.
Because of inharmonicity, a well-tuned piano has its treble a little sharp and its bass a little flat compared with exact equal temperament: this is stretch tuning. The curve O. L. Railsback measured in 1938 shows real tunings reaching about 30 to 35 cents at the ends. The Stretch curve option uses a conservative version: −20 cents at A0, −8 at A1, −3 at A2, zero from F4 to A4, +2 at A5, +6 at A6, +15 at A7 and +20 at C8. Every piano has its own inharmonicity, so treat the curve as a starting point.
Unisons, safety and when to call a professional
Two strings of the same key that are 1 Hz apart make the sound pulse once per second; this beating is what you listen for when setting a unison. In Unison mode the tool tells you whether the sound is steady or beating and estimates the beats per second. The classic method is to mute the neighboring strings with a felt or rubber wedge, set one string with the needle, then release the next one and adjust it until the beating disappears.
Turning pins without a proper tuning hammer and technique can strip a pin, crack the pinblock (the wood that holds the pins) or break a string, which is expensive to fix and can hurt you. A piano far below pitch, for example with A4 20 cents or more flat, needs a pitch raise: the technician brings it up gradually, in more than one pass, so the tuning holds. In those cases, call a piano tuner; the tool is still useful for checking the result.
Tips
- Measure in a quiet room and play every key with the same medium force: a very hard attack makes the note sharper for the first moments.
- In the bass, bring the device close to the piano and let the note ring for two seconds; reading from the partials needs about a third of a second of continuous sound.
- If your group plays at 442 Hz, change the Reference A before you start; every key then follows that A. To hear the reference A, use the online tuning fork.
- To see tenths of a cent on a note in the middle range, open the strobe tuner; to hear how each note should sound, use the online piano.
Frequently asked questions
Can you tune a piano with a phone app?
You can measure quite accurately: the phone shows how many cents each key is off and helps you check unisons and octaves. Moving the pins, however, takes a tuning hammer and technique; without them the risk of damaging the piano is real.
Does this replace a professional piano tuner?
No. It measures each key and lays out the order of the work, but a professional also takes care of how firmly the pins sit, sets unisons by ear, fits the octaves to that piano and notices problems with the action, strings and pinblock.
Why does the bass say “estimated from partials”?
Because the fundamental of the lowest strings is weak, especially on uprights, and a phone microphone picks up very little of the deepest sounds. The tool measures the strongest partials, corrects for the inharmonicity of the string and works out the fundamental from them.
What is the stretch curve? Should I turn it on?
It is the small departure from equal temperament that makes a piano's octaves sound clean. In the middle range it changes almost nothing. Turn it on if you want a target closer to a real tuning at the ends of the keyboard; the curve here goes up to 20 cents at most.
My piano is very flat. Can I bring it all up at once?
It is not recommended: raising many strings at once adds a lot of tension, old strings may break and the tuning will not hold. A technician does a pitch raise and then the fine tuning. Use the tool to measure how far below pitch the piano is and pass that on.
Does a digital piano need tuning?
No. Digital pianos and keyboards play recorded or synthesized sounds and do not drift out of tune. Some models have a master tuning setting (440 or 442 Hz, for example) in the menu; the tuner shows whether it is at the A you want.
How often should an acoustic piano be tuned?
Many technicians recommend one or two tunings a year, and more often for a piano that is played a lot or kept where humidity changes a lot. Checking a few A's from time to time shows when the piano starts to drift.