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A key signature is a symbol used in music notation telling you what key a song or piece of music is in. We haven’t started talking about keys just yet. There is a lot to discuss about keys and we will do that in later lessons. This lesson is just to explain key signatures used in written music. But, I’ll give you a little preview about keys so you can better understand key signatures.

What is a Key?

A key is the major or minor scale around which a piece of music revolves.

Every key has a unique set of seven notes. For example, the key of C Major uses the notes C, D, E, F, G, A, and B. The key of C Major uses no sharps or flats. It is the only major key using no sharps or flats.

As another example, the key of D Major uses the notes D, E, F#, G, A, B, and C#. The key of D Major has two sharps — F# and C#. Again, D is the only major key with two sharps.

As a third example, the key of Eb Major uses the notes Eb, F, G, Ab, Bb, C, and D. Eb Major has 3 flats — Bb, Eb, and Ab, and it’s the only major key with 3 flats.

What is a Key Signature?

The key signature is a group of sharps or a group of flats that tells you the key of the written music. The key signature shows the unique group of sharps or flats contained in the key. The key signature is written on the staff after the clef symbol and before the time signature.

There are 12 possible keys and 15 different key signatures for identifying them. At this point in the lessons don't worry about memorizing the keys just yet. We will cover them in more detail later.

Using our key examples above, the key of D would show 2 sharps as its key signature.

Key Signature for D Major

The key of Eb would show 3 flats as its key signature.

Key Signature for Eb Major

The key of C would show nothing since it has no sharps or flats.

Key Signature for C Major

With time and practice you will memorize all 15 key signatures. This will go hand in hand with learning scales and harmony.

How Do Key Signatures Work in Written Notation?

In music notation, the key signature tells the reader which notes to play sharp or flat throughout the music. If you are playing a song in a certain key, the same notes will be sharp or flat throughout the entire song. Instead of writing sharps or flats for each note every time it occurs in the music, the sharps or flats of the key are placed at the beginning of the music in the key signature. The reader is expected to remember to sharp or flat those notes as he or she plays.

In this example, you can see the notes of the D Major scale written without a key signature. Next to it is the very same notes using the key signature for D Major — 2 sharps. That means every F and C you encounter in the music are to be played as F# and C#. All key signatures work the same way.

D Major without and with key signature

The Order of Sharps and the Order of Flats

The sharps and flats of the key signature always follow a specific order and are always written in that order. There is a logic for this order, but we will look at this later.

The order of flats is: Bb, Eb, Ab, Db, Gb, Cb, Fb

The order of sharps is: F#, C#, G#, D#, A#, E#, B#

The Orders of Flats and Sharps

You might notice they are the same order of notes only reversed. When we discuss keys and harmony I will explain why you want to memorize these orders of flats and sharps. For now, it's enough that you know there is a specific order in which the flats and sharps are always written.

Key Signature Summary

This key signature system may seem like more work than less, but it’s not. As you begin to memorize keys like every musician should, you will see it makes more sense this way and written music is neater and easier to read. Once again, reading music will force you to learn the basics of music just a little bit better.