What a key is
A song's key is its home base: the note and chord that feel like “home”, plus the family of seven notes the melody and chords are mostly built from. In the key of G major, the chord G feels resolved and final, and the song naturally uses the chords G, Am, Bm, C, D, Em and F#dim. Knowing the key tells you which chords are likely to come next, which scale to solo with, and where to put a capo.
How the key finder decides
For each of the 24 major and minor keys, the tool checks every chord you entered:
- A chord that belongs to the key with the right quality (for example Em in G major) scores well.
- The major V chord in a minor key (E or E7 in A minor) also counts, because songs in minor keys borrow it all the time.
- Chords outside the key lose points.
- Songs very often start and end on the home chord, so the first and last chord get a bonus.
The top results are listed with a match percentage and the progression written as Roman numerals.
Relative major and minor
You'll notice G D Em C and Em C G D use exactly the same four chords. G major and E minor share the same notes — they are relative keys. What decides the key is which chord feels like home. That's why the order of chords matters: start and end on Em and the result leans to E minor; start on G and it leans to G major. Every major key has a relative minor three semitones below it (C → Am, G → Em, D → Bm, F → Dm).
Chords in every major key
| Key | I | ii | iii | IV | V | vi |
|---|---|---|---|---|---|---|
| C | C | Dm | Em | F | G | Am |
| G | G | Am | Bm | C | D | Em |
| D | D | Em | F#m | G | A | Bm |
| A | A | Bm | C#m | D | E | F#m |
| E | E | F#m | G#m | A | B | C#m |
| F | F | Gm | Am | Bb | C | Dm |
Why Roman numerals are useful
Writing I – V – vi – IV instead of G – D – Em – C describes the progression in any key. Upper case means major, lower case means minor. Once you know a song is I–V–vi–IV, you can play it in C (C G Am F), in D (D A Bm G), or anywhere else. Thousands of hit songs share this one progression. Our guide to chord progressions explains the most common ones, and how to find the key of a song shows how to do this by ear.
Frequently asked questions
Why does it show two keys with similar scores?
Usually they are relative keys (like C major and A minor) that share the same chords. Listen for which chord feels most like home — the one the song resolves to at the end of the chorus.
What if a song changes key?
Enter the chords of one section at a time. Many songs move up a semitone or tone for the last chorus; each section will show its own key.
What does the asterisk mean?
The chord root is in the key but the quality is different, for example a D major chord in A minor. These are borrowed chords and are common in rock and pop.