What key are these chords in?

One of my students likes to write chord progressions and the other day they asked me, “How do you figure out what key a chord progression is in?”

So I figured I’d type out my response to them here.

There are a few things we can do to figure out what key a chord progression is in. Ideally you’d use all of them together to figure out the key, but sometimes they may not all be useful.

Another reason to use multiple of these is because some chord progressions could be in two different keys. They likely aren’t in two keys at the same time, but a few chord progressions can fit into multiple different keys. So depending on specifically how the chord progression is set up and how the other music is written on top of it can determine which key it is in.

Here are the things we’ll be covering:

• Prior knowledge
• Write out the total notes
• What chord does it start and end on?
• What chord sounds like “home?”
• What other notes are in the music?
• Look for familiar chord progressions

Prior knowledge

In order to use most of these techniques you’ll have to know the notes of all of the major and minor scales. You’ll also have to know how to spell out the notes of major and minor chords. The more scales and modes you know and the more chords you can spell will help you more quickly identify the key of a song.

Some other knowledge you should have is a basic understanding of ear training. Knowing what the root note of a scale or chord sounds like will help. Knowing what the root chord of a scale will help.

Some basic knowledge of rhythms and measures and how to read music will help you better understand this article, though it’s not necessary to understanding the ideas presented here.

Write out the total notes

Take the chord progression and write out the total notes that you have. Include every note within each chord. Don’t repeat notes. Try to find at least one of each note name. You want an “A”, a “B”, a “C”, a “D”, an “E”, an “F”, and a “G.”

Let’s look at an example.

Here we’ve got a C major chord, an F major chord, and a G major chord. Now we need to find the total notes that we have.

C major has a C, E, and G. F major has F, A, and C. G major has G, B, and D.

If we list them in order we have C, D, E, F, G, A, B, and C. So now we have a guess. This song is likely in C major.

If we take another example we can guess based on how many sharps and flats we have.

Here we have an Eb major chord, an F minor chord, a Bb major chord and finally an Eb major chord at the end.

Eb major has Eb, G, and Bb. F minor has F, Ab, and C. Bb major has Bb, D, and F.

Before we put them all together, notice how many flats we have. We have three flatted notes; Eb, Ab, and Bb. What key has three flats?

If you guessed Eb major you’d be correct. If you guessed C minor you’d also be correct.

We can then guess that this chord progression is in Eb major because it has three flats, and it starts and ends on an Eb chord.

This brings us to our second method.

What chord does it start and end on?

Often chord progressions start and end on the “home” or root chord of the scale. In the above two examples those two chord progressions started and ended on the same chord. Those chords also happened to be the root chord of the scale.

This method won’t always be accurate so don’t use it by itself, but for a lot of tonal music it will be quite accurate.

This can also be used for melodies. If a melody starts and ends on a Bb then it’s a pretty good guess that the song is in Bb. Don’t use this alone because there will definitely be cases that you’ll be wrong, but it’s another way to guess.

What chord sounds like “home?”

This one gets a little harder to describe, but listening to the music intently can be a great way to learn about where the root of a scale might be. The chord built off of the root note of the scale will sound the most resolved. It’ll sound like the “home” chord, where the music wants to end. Other chords won’t sound resolved. Ending on the other chords will sound like the music hasn’t quite finished yet. We’ll call this the “I chord” (roman numeral one).

Listen to the music and try to hear what chord sounds the most resolved.

This can be useful if you’re trying to figure out a modal chord progression because the total notes may be the same group of notes as a major or minor scale, but the root of that scale doesn’t sound like the I chord.

This will likely line up with the beginning or ending chord, but might not always, so use your ears as best you can.

You can also use this with the melody. What notes sound the most resolved in the melody. There is normally one note that will sound the most resolved. Figure out that note as it will likely be the root note of the scale.

What other notes are in the music?

Another thing you can do, if the chords don’t give you all of the notes of a scale, is look for other notes in the music. If a song has all of the notes except one, you can likely guess using another technique, but if you’re missing two notes you might have to find some other notes in the music.

I normally like to look at the melody first. It’s the easiest voice to hear in most cases and will give you some other information.

If the melody has other notes that aren’t included in the chords, add those to your list of total notes and take another guess.

Look for familiar chord progressions

Looking for chord progressions that are familiar to you is a great way to figure out the key of a song. If you’ve learned a song in G major and you remember that chord progression, and you see another song with the exact same chord progression, it very likely will be in G major as well.

It can also be useful to know some common chord progression patterns. Knowing what a 12 bar blues chord progression looks and sounds like would be useful because that chord progression will have some added notes in it that aren’t in the major scale.

The same can be said about common chord progressions. Learning these in all 12 keys will require some music theory knowledge, but being able to recognize them can be useful.

That’s it for my tips on how to figure out what key a song is in. Give them a shot if you aren’t sure what key a song is in. Also realize that some songs may change key during the song. Some songs may have chords that are outside of the key. These are a little more complicated and beyond the scope of this article, but there will be other articles that I’ll write on those specific ideas.

ISJ