How to Determine the Key from Chords

You’ve picked out the chords of a song by ear — now what key is it in? Here’s how to figure it out.

Step 1: List All the Chords

Write down every chord in the song (or section). Include quality: C major, Dm, G7, etc.

Example: C – Am – F – G

Step 2: Try to Match Them to a Diatonic Set

A key has seven diatonic chords. If all or most of your chords fit within one key’s diatonic set, that’s likely the key.

C major diatonic chords: C, Dm, Em, F, G, Am, Bdim

All four chords (C, Am, F, G) fit within C major. Key = C major (or potentially A minor, the relative).

Step 3: Check for the Tonal Center

If both C major and A minor are candidates, listen to the last chord of a phrase. Which chord feels most final? That’s the tonic — and the key.

In C – Am – F – G, the phrase usually resolves to C, suggesting C major.

Step 4: Look for Non-Diatonic Chords

If a chord doesn’t belong to any single key, it might be:

• A borrowed chord (from the parallel minor)
• A secondary dominant (V of a non-tonic chord)
• A passing chord between two diatonic chords

Example: C – F – G – Ab — the Ab doesn’t belong to C major (bVII borrowed chord).

The Key Finder Tool

If you have a list of chords, the Key Finder tool will:

1. Calculate how many chords match each possible key
2. Show you the top candidates with match percentages
3. Link to the diatonic tool for the suggested key

This is useful when you have complex or chromatic progressions where matching by ear is difficult.

C Major vs. A Minor: The Relative Ambiguity

C major and A minor share all the same notes and chords. To distinguish them, listen for:

• Which chord starts or ends phrases (tonal center)
• Whether the progression builds tension toward C or resolves to Am
• Whether the 7th degree is raised (G# in A harmonic minor) — a distinctive signal

→ Use the Key Finder to analyze any chord set