Short answer: Listen for the bass note, decide whether the chord is major or minor, and use common chord progressions to narrow down the remaining possibilities.
If you have a song in your head and want to find the chords on the piano, you don’t need to search randomly across all 88 keys. The process becomes much easier when you divide it into three simple steps.
Step 1: Find the Bass Note
Start by listening to the lowest note in the music, especially on the first beat of a new chord. Hum that note, then find it on the piano.
If the note is G, the chord may be G major, G minor or another chord built around G. The bass note gives you a strong starting point, even though it is not always the root of the chord.
Step 2: Decide Between Major and Minor
Once you’ve found a likely root note, try playing the major chord. Does it fit the song, or does it sound too bright?
Then try the minor chord. In many cases, one of the two will clearly match the harmony better than the other.
Step 3: Use Common Chord Patterns
Pop and rock songs often use familiar groups of chords. If the first chord is C major, the next chord may well be F, G or A minor because those chords belong naturally to the same key.
Instead of testing every possible chord, begin with the most likely choices. The more common chord progressions you learn, the faster you’ll be able to work out songs by ear.
