How to find the key of a chord progression
Every song lives in a key: a home note and the seven-note scale around it. Chords built from that scale belong together, and spotting which scale they come from is one of the most useful reflexes a musician can have. It lets you transpose, improvise, and predict where a song is going.
A fast method
- Look at the odd chords out. A B♭ major chord in a progression of C, F and G? B♭ isn't in C major, so you need a key with a B♭, like F major.
- Check the ends. Progressions usually start and finish on the tonic chord, the chord that feels like home.
- Find the V. A dominant chord a fifth above the tonic (G or G7 in C) is a strong signal.
- Count accidentals. Match the sharps or flats in the chord names to a key signature.
Chords in a major key
Stacking thirds on each note of a major scale always gives the same pattern of chord qualities:
| Degree | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| In C | C | Dm | Em | F | G | Am | B° |
| In G | G | Am | Bm | C | D | Em | F♯° |
Notice that the G major key contains F♯°, not G♭. Spelling follows the scale: one letter per degree, so the seventh of G major is F♯.
Need all twelve keys at a glance? See the full chords in every key chart.
Minor keys
In natural minor the chords are i, ii°, III, iv, v, VI and VII. Songs often borrow the major V from harmonic minor (E instead of Em in A minor) because the raised seventh makes a stronger pull home. The drill treats that as part of the key. Higher levels throw in 7th chords, where the V7 is a big giveaway.
How to use this workout
Start in Warm-up until you're answering without looking at the hints. Move to Working set for minor keys, then Heavy lift for every key with 7th chords. A wrong answer shows exactly which chord doesn't belong to the key you picked, plus the Roman numerals of the correct key.
Frequently asked questions
How do I find the key of a chord progression?
List the notes in each chord and find the major or minor scale that contains all of them. In practice: check the first and last chords (they often name the tonic), look for a V or V7 chord a fifth above it, and use the key signature that matches the sharps or flats in the chords.
Why can a progression fit both a major key and its relative minor?
A major key and its relative minor share exactly the same seven notes, so C–F–G fits both C major and A minor. The tie is broken by which chord sounds like home. The drill avoids offering ambiguous pairs as answers.
Do I need to know key signatures first?
It helps, which is why Warm-up mode shows the number of sharps or flats under each answer. As you improve, hide the training wheels with the harder levels.