Music & Entertainment

Music 101: What Is A Key Signature? How to Read a Key Signature (Sharps and Flats)

Written by MasterClass

Aug 5, 2019 • 5 min read

Western music contains twelve distinct pitches, each of which is repeated over the course of many octaves. But most music does not utilize all twelve of these pitches within a single section. Typically only seven of the twelve pitches a regularly used within a section of music. So how do we identify which seven notes are available? By indicating a key and notating that key with a key signature.

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What Is a Key Signature?

A key signature is a visual symbol, printed on a musical staff, that indicates what key a section of music is written in. Key signatures are represented by using accidentals—better known as sharps and flats. The number of sharps or flats indicated in the key signature will tell the player what key the music is in.

What Is the Difference Between Key Signatures and Keys?

The difference between a key signature and a key is that a key signature is simply a printed symbol conveying information to a musician. The key that a section of music is written in will determine all sorts of things—most significantly, the notes and chords that will sound most harmonically consonant within that section of music.

Why Are Key Signatures Useful?

Key signatures are useful because they convey a great deal of information using only a single symbol. By simply glancing at a key signature, a musician can quickly tell:

  • What seven notes will be readily available to produce consonant harmony.
  • What consonant chords are available (the chords will be built upon the seven available notes).
  • Whether the piece has a major or minor tonality (this will also require glancing at a few bars of music, since every major key shares a key signature with a “relative minor” key. For instance, Bb major and G minor share a key signature.)

How to Read Key Signatures in Music

In a nutshell, a key signature tells you which notes you can play within a diatonic scale. Diatonic means “within the key.”

If you’re looking at a 5-line staff and you see no sharps or flats indicated, this means that the seven available diatonic notes are C, D, E, F, G, A, and B. It also specifically means you are either in the key of C major or A minor, because those are the two keys that contain no sharps or flats.

However, if you see any sharps or flats, this means you’re in a different key.

Sharp Key Signatures

In musical notation, sharps are the notes that are made high in a given key signature. The symbol for a sharp is #, which means half a tone higher than the written note. The first sharp key signature is the key of G, or its relative minor, which is E minor (Em).

  • These keys have a single sharp note: F#. The other six pitches are natural.
  • In the key of G, the notes in order are: G, A, B, C, D, E, and F#
  • In the key of Em, the notes in order are: E, F#, G, A, B, C, and D

To reach the next sharp key, we add an additional sharp note that is a fifth up from F#. That note is C#. We now have a scale that contains two sharps and five natural notes. This is the key of D, or its relative minor, which is B minor (Bm).

  • In the key of D, the notes in order are: D, E, F#, G, A, B, and C#
  • In the key of Bm, the notes in order are: B, C#, D, E, F#, G, and A

To continue through the sharp keys, we keep adding a sharp that is a perfect fifth higher than the previous sharp (for instance C# is a perfect fifth above F#). In turn, we end up in a key that is a perfect fifth higher than the one before it (for instance D is a perfect fifth above G). For this reason, sharp keys occur in what’s called the Circle of Fifths.

Here are the remaining sharp keys:

  • Three sharps. Sharp notes are F#, C#, G#. Produces the keys of A and F#m
  • Four sharps. Sharp notes are F#, C#, G#, D#. Produces the keys of E and C#m
  • Five sharps. Sharp notes are F#, C#, G#, D#, A#. Produces the keys of B and G#m
  • Six sharps. Sharp notes are F#, C#, G#, D#, A#, E#. Produces the keys of F# and D#m
  • Seven sharps. Sharp notes are F#, C#, G#, D#, A#, E#, B#. Produces the keys of C# and A#m

Flat Key Signatures

In musical notation, flats are the notes made low in a given key signature. The symbol for a flat is L, which means half a tone lower than the written note. The first flat key signature is the key of F, or its relative minor, which is D minor (Dm).

  • These keys have a single flat note: B flat (Bb). The other six pitches are natural.
  • In the key of F, the notes in order are: F, G, A, Bb, C, D, and E
  • In the key of Dm, the notes in order are: D, E, F, G, A, Bb, and C

To reach the next flat key, we add an additional sharp note that is a fourth up from Bb. That note is E flat (Eb). We now have a scale that contains two flats and five natural notes. This is the key of Bb, or its relative minor, which is G minor (Gm).

  • In the key of Bb, the notes in order are: Bb, C, D, Eb, F, G, and A
  • In the key of Gm, the notes in order are: G, A, Bb, C, D, Eb, and F

To continue through the flat keys, we keep adding a flat that is a perfect fourth higher than the previous flat (for instance Eb is a perfect fourth above Bb). In turn, we end up in a key that is a perfect fourth higher than the one before it (for instance Bb is a perfect fourth above F). For this reason, flat keys occur in what’s called Circle of Fourths.

Here are the remaining flat keys:

  • Three flats. Flat notes are Bb, Eb, Ab. Produces the keys of Eb or Cm
  • Four flats. Flat notes are Bb, Eb, Ab, Db. Produces the keys of Ab or Fm
  • Five flats. Flat notes are Bb, Eb, Ab, Db, Gb. Produces the keys of Db or Bbm
  • Six flats. Flat notes are Bb, Eb, Ab, Db, Gb, Cb. Produces the keys of Gb or Ebm
  • Seven flats. Flat notes are Bb, Eb, Ab, Db, Gb, Cb, Fb. Produces the keys of Cb or Abm

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