About the Song Key Finder
Enter the chords of a song or progression — for example "C G Am F" — and this key finder ranks all 24 major and minor keys by how well they explain those chords. It shows the most likely key, the runner-up, the Roman-numeral analysis of every chord, and which chords fall outside the key (borrowed or secondary chords).
It is useful when you want to jam over a song, transpose it, add a capo, pick a scale for a solo, or write a chord chart. Because a major key and its relative minor share the same chords (C major and A minor, for instance), the finder also looks at which chord the song starts and ends on and whether a major V chord appears, which is usually what decides between them.
The result is a best guess from the chord names alone: melody, bass line and context can change the answer, and modal or highly chromatic songs may not fit any single key perfectly.
How to use the song key finder
- 1Type or paste the chords in the order they are played.
- 2Read the most likely key and its fit percentage.
- 3Check the Roman numerals to see the function of each chord.
- 4If two keys tie, decide by which chord sounds like the resting point.
Formula and method
Each chord is reduced to its root and triad quality (major, minor, diminished, augmented; sus and power chords match any scale note). For every one of the 24 keys the tool counts how many chords belong to it: in a major key the diatonic chords are I, ii, iii, IV, V, vi and vii°; in a minor key it accepts the natural-minor chords i, ii°, III, iv, v, VI, VII plus the harmonic-minor V, vii° and III+ that minor songs commonly borrow.
Keys are ranked by the number of fitting chords. Relative major and minor keys always tie on that count, so tie-breakers reward the key whose tonic chord opens or closes the progression and whose dominant (major V) chord appears. Seventh chords are judged by their underlying triad.
- Fit
- Share of the entered chords that belong to the key
- *
- Chord outside the key (borrowed, secondary dominant, etc.)
Worked examples
Pop progression C – G – Am – F
All four chords belong to both C major and A minor. Starting on C and containing G (the V of C) tips it to C major, giving the classic I–V–vi–IV.
Same chords starting on Am
The chords are the same, but the progression starts and ends on Am, so A minor scores the extra tie-breaker points: i–VI–III–VII–i.
Minor key with harmonic V: Dm Gm A7 Dm
A7 is not in F major (whose iii is Am), but it is the harmonic-minor dominant of D minor. With Dm at both ends, D minor fits all four chords.
Borrowed chord: G Bb C G
G and C fit G major, but B♭ does not — it is the ♭III borrowed from G minor, common in rock. G major still wins with 3 of 4 chords and tonic at both ends.
Frequently asked questions
How do I find the key of a song from its chords?+
List the chords and find the key whose diatonic chords contain all or most of them. Then check which chord the song starts and ends on — that chord is usually the tonic. This tool automates both steps across all 24 keys.
Why does it say C major when the song feels like A minor?+
C major and A minor use exactly the same chords. The tool chooses using the first and last chords and whether E or E7 (the major V of A minor) appears. If your song centres on Am, start the list with the chord that feels like home.
What does a chord outside the key mean?+
Many songs borrow chords from the parallel key (like B♭ in G major) or use secondary dominants (like D7 in C major). A few outside chords are normal; many usually means the song changes key.
Can it detect modes like Dorian or Mixolydian?+
It reports the parent major or minor key. A Mixolydian song on G (G F C) shows as C major or G major with F outside; a Dorian song on D (Dm G) shows as C major or D minor. Use the scale generator to explore the mode.
Do seventh and extended chords work?+
Yes. Cmaj7, Dm7, G7, F#m7b5, Asus4, D/F# and C9 are all recognised and judged by their underlying triad; slash bass notes are ignored.