Key Signatures - My Music Theory (2025)

Key

When we write music which mostly uses notes from the scale of C major and sounds good finished with a C, we say that the music is “in the key of C major” or “in C a major”.

Here’s a short tune in C major:

For ABRSM Grade One Music Theory, you only need to know about these three key signatures: G major, D major and F major, and for TrinityGrade One Music Theory you need to know G and F.(And you need to know that C major doesn’t need a key signature!)

G Major Key Signature

If a tune mostly uses the notes from the G major scale and sounds good finished with a G, then the music is “in G major”.

The scale of G major contains the notes G-A-B-C-D-E-F#. The key of G major contains F sharps, not F naturals.

Instead of writing all the Fs in the piece with sharp signs next to them, we write just one F sharp, right at the beginning of the line, after the clef and before the time signature.

This is called the “key signature“.

In the treble clef, we always write the F sharp sign on the top line (we never use the lower F space). You should be able to just see the line of the stave between the two horizontal lines of the sharp sign.

In the bass clef, we write the sign for F sharp on the second line from the top.

The key signature is written at the beginning of every line of music, immediately after the clef, to remind us that all the Fs need to be F sharps.

(We don’t use a key signature for music which is in C major, because we don’t need one! – C major doesn’t have any sharps or flats!)

The key signature is there to remind us that all the F’s in the piece should be F#s. It applies to ALL the pitches of F, not just the one on the top/2nd line of the stave.

Here’s the same tune as above, but now it’s in G major:

F major Key Signature

Let’s look at the key signature for F major next. Remember that in F major there aren’t any sharps, but there is one flat – B flat.

In the treble clef, the flat is written on the middle line.

In the bass clef, the flat is written on the second line from the bottom.

D Major Key Signature (ABRSM Grade 1, Trinity Grade 3)

Finally, let’s look at D major:

(T=tone or whole step, S=semitone or half step).

The scale of D major has two sharps – F sharp and C sharp. This means that music written in the key of D major has F#s and C#s too.

The key signature of D major in the treble clef looks like this:

We add the C sharp after the F sharp that we’ve got already.

In the bass clef, the key signature of D major looks like this.

Key Signatures Exercises

Point your mouse at the staves (tap on mobile devices) to reveal the answers.

Naming Key Signatures

Name the major keys shown by these key signatures.

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2.

Writing Key Signatures

Add the correct key signatures to these bars.

1.

2.

3.

Reading Key Signatures

Give the letter name of each of the notes marked *, including the sharp or flat sign where necessary.