How to Determine the Key from Chords

You’ve picked out the chords of a song by ear, and now you want to name the key. Take C – Am – F – G. All four chords live inside C major, so the key is almost certainly C major (or its relative, A minor). The trick is knowing how to check that quickly, and how to break the tie when two keys both fit.

Hear it first

Before working through it on paper, let the tool do the matching.

1. Open the Key Finder
2. Type C Am F G into the text field
3. Press Analyze in the dock
4. Read the ranked results: listen for which key the tool puts on top, and how high the match rate climbs

When several keys score close together, that overlap is your cue that you’re dealing with relative keys, not a wrong answer.

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).

Letting the Tool Do the Matching

Checking every chord against all 24 keys by hand is tedious, and chromatic progressions make it worse. The Key Finder counts how many of your chords match each possible key, ranks the candidates by match rate, and links each result to its diatonic chord table. Use it as a fast first pass, then confirm the tonal center by ear.

C Major vs. A Minor: The Relative Ambiguity

C major and A minor share all the same notes and chords, so a match score alone won’t separate them. Listen for these instead:

• Which chord opens or closes a phrase (the tonal center)
• Whether the progression builds toward C or settles onto Am
• A raised 7th — a G# in A harmonic minor is a clear minor-key fingerprint

What to try next

Take a song you’ve already transcribed and run its chords through the tool, then cover the screen and predict the key yourself before checking. After a few songs you’ll start spotting the tonic before the tool finishes ranking.

→ Analyze a chord set in the Key Finder