How to identify a chord from its notes

To name a chord, rearrange its notes so they stack in thirds, take the bottom note of that stack as the root, and measure the gaps above it: 4 then 3 semitones is major, 3 then 4 is minor, and an extra third on top makes it a seventh chord. If the lowest note you actually played is not the root, the chord is an inversion and gets a slash name such as C/E. The chord finder does this instantly from keys you click or note names you type, but the method is worth knowing for when you only have a pencil.

Stack the notes in thirds

Write the note letters in any order and drop duplicates; a guitar chord often doubles notes, and doubled notes do not change the name. Then rearrange the letters so each is two letters above the last, skipping one letter each time: C to E, E to G, G to B. For example, the notes E, C and G become C, E, G. The notes F, A, D become D, F, A. A four-note set such as B, D, G, F becomes G, B, D, F. The bottom of the tidy stack is the root.

Measure the intervals

Count semitones from the root to each note above it, then match the pattern:

• 4 and 7 semitones: major (C, E, G).
• 3 and 7: minor (D, F, A is D minor).
• 3 and 6: diminished (B, D, F).
• 4 and 8: augmented (C, E, G♯).
• 4, 7 and 10: dominant 7th (G, B, D, F is G7).
• 4, 7 and 11: major 7th; 3, 7 and 10: minor 7th.

Without counting keys, the interval calculator names the gap between any two spelled notes, and Music intervals explained: names, semitones and inversions covers why a third can be major or minor.

Check the bass note

The lowest note you hear matters. If it is the root, the chord is in root position and takes the plain name. If it is another chord tone, the chord is inverted: C major with E at the bottom is written C/E, and with G at the bottom C/G. Songwriters also use slash chords where the bass note is not in the chord at all, such as C/B♭ on a descending bass line. That is why the chord finder treats the lowest key you click, or the first note you type, as the bass, and ranks names with the root in the bass first.

When notes have two names

Some note sets stack in thirds two ways. A, C, E, G is A minor 7th, but it also contains C major with an added 6th (C, E, G, A), so it can be read as C6 with A in the bass. Which name is right depends on context: if the bass plays A and the song is in A minor, call it Am7. A diminished seventh chord is even more ambiguous, because its four notes are spaced evenly and any of them can act as the root. That is why the chord finder lists every matching name rather than pretending there is only one, with the most common reading first.

Missing and extra notes

Real voicings often leave things out. The fifth is the note most often dropped, especially in seventh and ninth chords, because it adds little colour; C, E and B♭ is still heard as C7. A chord with only a root and fifth, such as E and B, has no third and so is neither major nor minor: it is a power chord, written E5. Going the other way, notes stacked beyond the seventh become extensions: the ninth is the second an octave higher, so C, E, G, B♭, D is C9. If two notes a semitone apart refuse to fit any stack, you may be looking at a passing note or a scale fragment rather than a chord.

Identifying chords by ear

Working by ear uses the same steps. First find the bass note, because it is usually the root. Then decide whether the chord sounds bright (major) or darker (minor), and listen for the extra tension of a seventh. The piano chord chart and the guitar chord chart let you play candidate chords until one matches what you hear, and the ear trainer builds the interval recognition that makes this faster. For more on the shapes themselves, see Piano chords for beginners: how to build any chord. The honest limit for any finder, human or software, is context: the same notes can be different chords in different songs.