Learning how to work out the key of a song helps you understand which notes and chords are likely to fit it. In this article, we’ll use two short examples, one in G major and one in E minor, to explore how musical keys work.
So, What Is a Key?
A musical key tells you which notes and chords are commonly used in a piece of music. It also helps you understand which note feels like the main resting point.
This note is called the tonic. You can think of it as the musical note that sounds like a natural place to finish.
Take C major, for example. The C major scale has seven notes:
C – D – E – F – G – A – B
In the key of C major, C is the tonic. A melody in C major might finish on C, and the music will often settle on a C major chord at the end of a phrase or song.
Most of the notes and chords in a song in C major will come from the C major scale. However, composers sometimes use notes outside the scale to add colour, create tension or lead into another section of music.
Knowing the key helps you understand why certain notes and chords work well together.
To learn more about how major scales are formed, read our guide to major scales and keys.
How to Work Out the Key of a Song Using the Key Signature
When learning how to work out the key of a song, one of the first things to check is the key signature. It consists of sharps (♯), flats (♭), or sometimes no sharps or flats at all. You’ll find it just after the clef and before the time signature.
For a closer look at how key signatures work, see our guide to key signatures and how they work.
Here are a few examples:
- C major and A minor: no sharps or flats.
- G major and E minor: one sharp, F♯.
- D major and B minor: two sharps, F♯ and C♯.
- F major and D minor: one flat, B♭.
Each of these key signatures can belong to either a major key or its relative minor key.
For example, G major and E minor both have one sharp, F♯, but they’re different keys.
How can two keys share the same key signature but sound different? Let’s use G major and E minor to find out.
Understanding Major and Minor Keys
Some music sounds bright and cheerful, while other music sounds darker or more serious. One reason for this is whether the music is in a major or minor key.
Major keys are often associated with a bright or uplifting sound, while minor keys can sound darker or more reflective. These are general impressions rather than strict rules, of course. Music can express all sorts of emotions in either type of key.
It also depends on how the notes are arranged around the tonic.
Let’s return to our two examples: G major and E minor.
The G major scale is:
G – A – B – C – D – E – F♯
The E natural minor scale is:
E – F♯ – G – A – B – C – D
As you’ll notice, both scales contain exactly the same seven notes. The difference is that G major starts on G, while E natural minor starts on E.
G major and E minor are known as relative keys. They share the same key signature, but the music centres around G in G major and E in E minor. This is what gives the two keys their different characters.
So, if you see one sharp in the key signature of a piece of music, it doesn’t necessarily mean the piece is in G major. It could be in E minor instead.
Hear the Difference: G Major vs. E Minor
One way to understand how to work out the key of a song is to compare two short pieces of music: one in G major and one in E minor.
Both pieces use the same seven notes and have the same key signature: one sharp, F♯. However, one is in G major and the other is in E minor.
Listen to how the two pieces sound. Notice how the melody and chords are arranged around different tonic notes, giving each piece its own character.
Example 1: G Major
This piece is in G major.
The chord progression is:
G major – C major – D major – G major
The progression starts and finishes on G major. The D major chord creates a sense of movement before the music returns to G major. The melody also finishes on G, helping the piece feel complete.
The G major scale is:
G – A – B – C – D – E – F♯
These are the notes that form the foundation of the key. If you’re learning to improvise in G major, they’re a useful starting point for creating melodies that fit the music.
Example 2: E Minor
This piece uses the same seven notes as the first example, but it’s in E minor.
The chord progression is:
E minor – C major – D major – E minor
The C major and D major chords appear in both examples, but this piece starts and finishes on E minor rather than G major. This makes E the tonic and gives the music a different character.
The E natural minor scale is:
E – F♯ – G – A – B – C – D
Compare this with the G major scale above. The notes are the same, but E is the tonic here rather than G.
Although the two pieces use the same seven notes, they sound different because G is the tonic in one and E is the tonic in the other.
How Keys Relate to Chords
I mentioned earlier that knowing the key of a piece of music helps you understand which notes and chords are likely to fit it.
A chord is made up of notes played together. In a particular key, some chords naturally work well together because they use notes from the same scale.
If you’d like to learn how to work out the chords in a major key, read our guide to working out the chords in any major key.
For example, in G major, three commonly used chords are:
- G major
- C major
- D major
In E minor, you’ll often find:
- E minor
- C major
- D major
You’ll notice that C major and D major appear in both examples. This is because G major and E minor share the same seven notes.
The difference is how the chords relate to one another and which chord sounds like a natural place to finish.
In our G major example, the progression G–C–D–G begins and ends on G major. In the E minor example, Em–C–D–Em begins and ends on E minor.
Even though some of the chords are the same, they play different roles in each key. Once you understand this, it becomes easier to see why a chord progression works in one key and how you might use similar chords in your own music.
Why Knowing the Key Matters
Knowing how to work out the key of a song can help you read sheet music, learn songs, improvise and write your own music.
Here are some examples:
- Reading sheet music: The key signature tells you which notes are sharp or flat, helping you read the music correctly.
- Learning songs: Understanding the key gives you a clearer picture of the notes and chords used in a song.
- Improvising: Knowing the key gives you a sensible starting point when choosing notes for a solo or melody.
- Writing your own music: Knowing the key helps you understand which notes and chords work well together, making it easier to create your own melodies and chord progressions.
Want to learn more about music theory? Explore our other music theory articles for more helpful explanations and practical tips.