How to Find a Song's Key From Its Chords: Identifying the Original Key

What knowing the key makes easier

• Deciding whether to spell transposed chords with sharps or flats
• Working out which capo fret gives easy shapes
• Narrowing the next likely chord down to seven candidates when playing by ear
• Knowing which notes (scale) work for improvising or harmonising

Finding the key looks like it needs music theory, but when you have a chord sheet, the basic method is to check “which key's diatonic chords fit the most chords” — something you can do mechanically with a chart.

Three clues for finding the key

1. 1

   Find the key whose diatonic chords fit

   Compare the chords in the song with the diatonic chords of the 12 keys. “G D Em C” fits entirely in G: G (I), D (V), Em (VIm), C (IV). C, Em and G also fit the key of C, but D isn't Dm there, so C is ruled out.

2. 2

   Look at the first and last chords

   Songs often start and end on the key's tonic chord (I). If two or more keys are still possible, choose the one where the first and last chords are I. The chord at the end of the chorus or of the whole song is an especially strong clue.

3. 3

   Decide between major and minor

   If the song starts and ends on VIm (Am in the key of C) and keeps feeling like it comes home to Am, it's in the relative minor (A minor). If it ends on I, it's major.

The diatonic chord chart and how to read scale degrees are covered in the diatonic chords chart.

Worked examples

Some progressions, like “F G Em Am”, never use the tonic (C) at all. Even so, only one key contains all of them among its seven diatonic chords, so you can call it C. The fewer chords you have, the harder it is to narrow down, so use as many chords as possible — from the verse through the chorus.

Progressions that are easy to misread

• Key changes: if only the chorus moves up a semitone or a whole tone, find the key of the verse and the chorus separately
• Borrowed chords: when chords borrowed from the parallel minor appear, like B♭ or Fm in a C-major song, more chords fall outside the chart
• Secondary dominants: E7 (heading to Am) or D7 (heading to G) in a C-major song are common even though they're not diatonic
• Songs that start on IV: with progressions that don't start on I, like “F G Em Am”, don't decide from the first chord alone
• Phrases ending on V: when the end of the first verse or the bar before the chorus stops on V, it's easy to mistake it for the end of the song

With only about four chords, a progression can sometimes be read in two keys. For example, “B E F#m G#m” fits entirely in E (V, I, IIm, IIIm), but because it starts on B it's sometimes taken as B. In cases like this, decide by the song's final chord or the chord that sounds most settled.

Once you know the key, make the chord spelling consistent. Major keys F, B♭, E♭, A♭ and D♭ and their relative minors (Dm, Gm, Cm, Fm, B♭m) use flats; major keys G, D, A, E and B and their relative minors (Em, Bm, F#m, C#m, G#m) use sharps. If a chord sheet mixes D# and E♭, one of them is spelled against the key you found. Knowing the key helps you spot that kind of inconsistency.

Confirming by ear, and using the tool

To check whether the key you found is right, play its tonic chord while listening to the song. If the tonic sounds settled at the end of the song, you're right. If not, try the tonic of another candidate or the VIm of the relative minor.

1. 1

   Paste the chord sheet

   Paste a chord sheet into the “Transpose” tab of the Chord Transposer & Capo Calculator and it detects the original key automatically, from how the chords fit the diatonic chords and from the first and last chords.

2. 2

   Fix it by hand if it's wrong

   Detection can be off in songs with many key changes or borrowed chords. You can pick the original key yourself from all 24 major and minor keys, and the sharp/flat spelling after transposing follows that key.

3. 3

   Play the tonic to check

   Tap a chord to hear it, then play the I of the detected key and check that it fits the end of the song.

Once you know the key, see how to transpose chords to move it to a comfortable singing pitch, and the capo chart for an easy capo position. If you play shamisen or sanshin, the method for converting a key into the instrument's pitch number is in how to find the shamisen pitch number.

FAQ

How do I find a song's key from its chord progression?

Look for the key whose diatonic chords contain the most chords in the song; if several fit, choose the one where the first and last chords are I. If the song starts and ends on VIm, it's in the relative minor.

Is “Am F G C” in A minor or C major?

It's usually read as C. The chords fit both keys, but ending on C makes it sound like a major-key phrase. A progression that ends on Am would be read as A minor.

How do I tell major from minor using chords?

Relative keys (C and Am, G and Em…) share the same chords, so look at which chord is the centre. Starting and ending on I means major; starting and ending on VIm means minor. A major V chord (E or E7 in an A-minor song) makes minor more likely.

How can I check that I found the right key?

Play the tonic chord of the key you found along with the end of the song. If it sounds naturally settled, you're right. If it sounds off, try another candidate or the tonic of the relative key.

How do I find the key of a song that modulates?

Split the song before and after the key change and analyse each part separately. Many songs move up a semitone or whole tone just for the chorus, so analysing the chorus chords on their own makes it easier to tell.