I always thought this was the world's biggest Piano.. [They started making these in 1909 ... see story below...]

Bösendorfer built the first Imperial in 1909, following a suggestion by composer Ferruccio Busoni to build a model with an extended range. Busoni sought to extend the range to accommodate his transcription of Johann Sebastian Bach's organ works. In order to emulate the 32 foot registers available on some large organs, he needed the entire octave down to C0. The "290" Bösendorfer Imperial Grand features 97 keys: a full eight octaves. This is in contrast to their other extended model, the Bösendorfer 225, which has 92 keys (down to F0). The extra keys, which are all at the bass end of the keyboard (that is, to the left), are colored black so that the pianist can tell them apart from the normal keys of an 88-key piano. They were originally covered with a removable panel to prevent a pianist from accidentally playing the extra notes. While the keys are seldom used, the extra bass strings create additional harmonic resonance that contributes to an overall richer sound. Compositions have been written specifically to utilize the extra keys. Pianist and University of Washington School of Music director Robin McCabe explains the challenge of adjusting to the extra keys: "One's 'southern sight-lines,' so to speak, can be seriously skewed because of the extra footage in the bass. Ending a piece such as Debussy's L'isle joyeuse, for example, with its nose-dive final gesture to the low A of the piano, becomes a bit more problematic when that A is not the lowest note on the piano!" Reportedly, "the 290 has proved a bit of a temperamental star, sounding harsh and jarring in the hands of pianists who don't understand how to play it, and marvelously refined in the hands of those who do".[From Wikipedia]
- [note - I didn't have any trouble accomodating the extra bass notes in some of these conpositions on the page above...]

But then this one-of-a-kind showed up from China: [88 notes]

But then, no, this one below apparently the biggest (18' 10")
one-of-a-kind 88 notes... It was built by a 15 year-old boy... [with a little help]
~ It's so big the bass section has all unwound strings ~
Certainly a crowning achievement for any age, but 15???
See the inventor's YouTube Video »