How to Find the Key of a Song on Guitar

Knowing a song's key is useful for several things at once - from picking a pentatonic position for a solo (see [[connecting-scales-and-chords:the article on connecting chords and scales]]) to figuring out chords by ear. You can find it without trained musical ears, using a few practical signs.

Sign one: the last chord of the song

Songs almost always end on the chord of their key - that's the simplest and most reliable first clue. If the last chord of a verse or the whole song is Am, there's a good chance the key is A minor (or C major - see the next point on relative keys).

Sign two: the chord that feels like it wants to be the last one

Even without theory, it's usually clear by ear which chord in a progression sounds like 'home' - there's a sense of resolution on it, like the phrase has finished rather than being left hanging. That's almost always the key's tonic chord, even if the song doesn't actually end on it.

Relative major and minor share the exact same chords

Every major key has a relative minor with the exact same set of chords (C major and A minor is the most common example - see the article on CAGED for how that lays out on the neck), which is why the same chord list alone doesn't give a definitive answer - only combined with the 'where does it feel like home' sign.

Sign three: the full list of chords in the song

Write out every chord used in the song - in the vast majority of cases they all fit inside one key (see the article on 10 chords). If one chord clearly doesn't fit with the rest, that's either a sign of a key change within the song or a borrowed chord from outside the key - both are rarer than a simple, single-key song.

Why the key matters in practice

Once you know the key, it's immediately clear which pentatonic position or scale to play over the accompaniment for a solo (see the article on getting started improvising), instead of hunting for notes one at a time. This isn't a theory exercise - it's a direct practical shortcut into improvising.

Try it in practice

Open chord trainer