The hardest classical piano pieces, measured

Every list of hard piano pieces is someone's opinion. La Campanella, Islamey, the Hammerklavier, the same names in the same order, with nothing behind the ranking except that everyone agrees.

We had a reason to measure instead. Klaviero charts classical pieces note by note, with both hands separated, so a computer can play them back and judge a human against them. That means we have the actual note data for 4,296 pieces: 2,907,841 notes across 167.7 hours of music by 320 composers.

So here is difficulty with a number attached.

The measure

For each piece we take the busiest 25 seconds anywhere in it and divide the note count in that window by 25. That gives peak notes per second.

25 seconds is chosen deliberately. A one-second window rewards a single loud chord, which tells you nothing. 25 seconds is long enough that only sustained density survives, which is what actually exhausts a pianist.

This measures one thing: how many notes arrive, how fast. It does not measure stretch, it does not measure jumps, it does not measure musicianship. A piece can be brutally hard and score low. It is one axis, honestly labelled.

The densest twenty in the library

This table is piano only. The library also holds guitar, organ, choral and koto charts now, and a Sor study is not a hard piano piece however many notes a second it carries. Where a chart is an ensemble, the figure counts the part you are judged on, not the twelve instruments playing behind it.

Four things the data says that the opinion lists do not

Two sequences of La Campanella agree

The library holds La Campanella twice, from two separate sequences. One is a public-domain import, the other is Bernd Krueger's from piano-midi.de, filed under the Grandes Études de Paganini as No. 3. The first is 4,064 notes and peaks at 28.3 notes per second. The second is 4,144 notes and peaks at 27.9. They land within about 2% of each other on both counts.

Length and density are different problems

Chopin's Prelude Op. 28 No. 12 is 1,243 notes and it is over in 0:57, and it ranks 32 of 4,296 for density. Beethoven's Ninth finale is 13,924 notes, eleven times as many, and it is less dense at 24.3. One will wreck your hands in a minute. The other will wreck your concentration over 21:16.

La Campanella is famous for the wrong reason

It ranks 29 of 4,296 at 28.3 notes per second, which is genuinely near the top, but its reputation comes from the jumps rather than the density. The Hungarian Rhapsody No. 2, which everyone thinks of as showy rather than hard, is denser.

The gentlest famous pieces are gentler than you think

Satie's Gnossienne No. 3 peaks at 2.7 notes per second, which is one note every 370 milliseconds at its busiest moment. Schumann's Träumerei is 4.1. These pieces sound accomplished and sit in a range a beginner can reach.

The other end

Where the numbers come from

Each piece is a chart: a list of notes with a time, a duration, a pitch, a velocity and a hand. The peak figure is a rolling 25 second window over the note onsets, taking the maximum. Nothing is estimated and nothing is rounded up.

The full table for all 4,296 pieces is at the catalogue, sortable.

If you want to use this data, take it. Link back here and we are square.

What this has to do with us

Klaviero is a falling-notes piano game for MIDI keyboards. The measurements exist because the game needs them: to grade difficulty, to size the timing windows, and to tell you what you are walking into before you start a piece.