Piano Keys: Theory, History, and Secrets Unlocked

Graphic by Jay Alan Zimmerman.
Piano keys are an iconic image for music throughout the world, but they represent much more than sound. While their distinct arrangement of white and black have been featured in paintings, sung about by pop singers, and reproduced on everything from napkins to neckties—these keys are not only visual reminders of a piano. They hold a history spanning thousands of years. They connect to the scientific study of vibrations, to mathematical equations, and put the entire musical spectrum of human hearing under your fingers. If you love music, then it’s time to let the piano keys unlock their hidden mysteries.

The White Keys


Representation of the hydraulis (second from left) and other instruments in the Zliten mosaic from ancient Rome.

When we see piano keys we tend to think of a piano, but pianos are a relatively young invention. The piano keyboard descended from the harpsichord, which descended from a combination of a stringed harp and the keys of a pipe organ. So to find the origin of piano keys we must trace the evolution of a pipe organ all the way back to the third century B.C.E. In ancient Greece, the first musical keyboard device was called a hydraulis—meaning “water organ.” This instrument used the power of water to blow air through the pipes of a pan flute.

The seven white piano keys named A, B, C, D, E, F, G reflect the seven basic notes of the hydraulis. These notes were all the ancient Greeks needed because their tones create natural diatonic scales: a major scale when starting on C and a minor scale when starting on A—still the two most commonly used scales in western music. The sound of the hydraulis made it a very popular instrument throughout the first five centuries A.D. But as other cultures and new ideas expanded the complexity of music beyond simple folk music and Gregorian chants, musicians needed more than a diatonic scale. It was time to get chromatic.

The Black Keys

In the 14th century, five new keys were added to the original seven, creating what is called a chromatic scale. On the modern piano, these are called “sharps” and “flats” and colored black. But on some early organs and harpsichords, the colors were reversed. The oldest documented keyboard that used the seven-plus-five keyboard is the German Halberstadt organ of 1361.

Since the original seven white keys created natural major and minor scales consisting of two half-steps and five whole steps, the new black keys were slipped in between the whole steps to make 12 equal half-steps. Over time, the tuning of these keys were mathematically refined into what is called an “equal-tempered scale”—allowing musicians to play accurate major and minor scales starting on any of the 12 notes.

The Piano Keys in Octaves

By the time these black and white keys had migrated from the pipe organ to the harpsichord and finally to the 18th century invention called a piano, the keyboard had grown not only from seven scale tones to 12, but also multiplied into octaves and sections.


Replica of an 1805 fortepiano made by Paul McNulty.

An “octave”—just like an octagon and an octopus—relates to the number eight. In the original seven white key scales, an octave was the eighth note: twice as high as the starting note—or twice as low when playing downward. Mathematically and scientifically, the higher note in every octave is exactly double the frequency in pitch, or “hertz.” Hertz measures sound vibrations in cycles per second. So the orchestra tuning note of A 440 hertz creates a vibration that cycles 440 times in a second. And since each octave is double the octave below, the next higher A is double the hertz (880) and the next lower A is half (220). On the frequency-pitch conversion chart above, you can see how the hertz of every note on the piano has a mathematical relationship to every other note.

The number of octaves found in the earliest keyboard instruments were often limited to three or four, but this quickly grew to a bit more than five octaves throughout the Renaissance, Baroque, and Classical periods of music. This is why playing music from those eras never requires piano keys at the upper or lower extremes of the modern piano. Sometimes you’ll find passages in Mozart piano pieces that seem to want to go higher, but Mozart couldn’t because his keyboard ran out of notes!

The Piano Keys in Sections

As the Classical era shifted into the Romantic era—from Mozart to Beethoven—the number of piano keys kept growing, until it reached our familiar 88. This modern arrangement of 52 white keys and 36 black keys provides nearly eight octaves. Today each key is not only named A through G for its tone in the scale, but also one through eight for its octave. These range from the lowest C (C1) to the highest note (C8), with the three extra low notes numbered octave “zero.”

Near the middle of the piano is “middle C”—also called C4 because it is in the fourth octave. This note serves as the dividing point between the lower bass section (musically notated on a bass clef) and the upper treble section (notated on a treble clef). With C4 “middle C” as a guide, it’s easy to visualize the four octaves used in most vocal music, from a soprano’s high C (C6) down to a bass’s low C (C2).

But even 88 keys are not enough for some. You can have a full eight octaves on some Bösendorfer pianos, which expand down to C0 (zero). There are even a few pianos that expand up to F8, providing 102 piano keys.

Using the Piano Keys

Looking over this familiar field of black and white, you can see the natural visual rhythm of the seven-plus-five design. This arrangement lets you quickly spot sections and octaves, easily allowing combinations of mathematically related frequencies to create harmony or clustering half-steps together to create the sounds of dissonance. By focusing on the white keys, you can go back in time and replicate the music of the ancient Greeks. Or by using the black keys, you can explore the pentatonic (five-note) scales of Eastern cultures. It’s this unique blend of cultures, history, math, science, and visual rhythm that makes piano keys so alluring, iconic, and of course—the keys to creating exciting music.

Piano Keys by the Numbers
88 keys on most pianos
52 white keys
36 black keys
8 octaves for A, B, C, and B-flat (or A-sharp)
7 octaves for D, E, F, G, and D-flat, E-flat, G-flat, and A-flat
7 white keys named A, B, C, D, E, F, G
5 black keys with two names each: A-flat/G-sharp, B-flat/A-sharp, D-flat/C-sharp, E-flat/D-sharp, G-flat/F-sharp
2 main sections split the keyboard into bass and treble
1 note in the middle called “middle C”
0 is the octave number given the three lowest notes
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Copyright © 2017 Nancy M. Williams. All Rights Reserved.

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