How to Name a Seventh Chord From Its Root, Third, Fifth, and Seventh

A seventh chord contains four distinct chord tones that can be arranged in a stack of thirds. Its members are called the root, third, fifth, and seventh. Adding a note a third above a triad’s fifth produces this structure, as explained in “Introduction to Seventh Chords” from Music Theory for the 21st-Century Classroom.

If the root and chord members are already labeled, preserve those labels. Otherwise, arrange the note letters into alternating-letter order. For example, the notes E–G–B–C can be rearranged as C–E–G–B: root C, third E, fifth G, seventh B. Keep every sharp, flat, or natural attached to its note.

For now, write this analytical stack without worrying about which note is lowest in the actual performance. You will add the bass information after identifying the chord.

Measure the third, fifth, and seventh from the root, rather than measuring each one from the preceding chord tone. Two practical methods are comparing the notes with the root’s major scale or counting semitones. Both methods are described in “How to Identify Perfect, Major, and Minor Intervals”.

For the major-scale method, imagine a major scale beginning on the chord root. Its third and seventh are major intervals; its fifth is perfect. Lowering the major third or major seventh by one semitone makes that interval minor. For example, D major contains F♯, A, and C♯: D–F is therefore a minor third, while D–C is a minor seventh.

Use this compact semitone reference when checking your result. Count the root as zero and each movement to the next adjacent piano key as one semitone. The standard counts are given in the interval-identification lesson; diminished intervals follow the rules in “Augmented and Diminished Intervals”.

Chord member	Interval quality	Semitones above root
Third	Minor third	3
Third	Major third	4
Fifth	Diminished fifth	6
Fifth	Perfect fifth	7
Seventh	Diminished seventh	9
Seventh	Minor seventh	10
Seventh	Major seventh	11

The spelling still matters. A semitone count checks the distance, while the note letters establish whether you are naming a third, fifth, or seventh. This becomes especially useful with diminished sevenths.

The following table combines the five common interval patterns listed in Open Music Theory’s seventh-chord reference. Here, M means major, m means minor, P means perfect, and d means diminished. All intervals are measured above the root.

Third	Fifth	Seventh	Resulting quality	Example notes	Symbol
M3	P5	M7	Major seventh	C–E–G–B	Cmaj7
M3	P5	m7	Dominant seventh	C–E–G–B♭	C7
m3	P5	m7	Minor seventh	C–E♭–G–B♭	Cm7
m3	d5	m7	Half-diminished seventh	C–E♭–G♭–B♭	Cm7♭5 or Cø7
m3	d5	d7	Fully diminished seventh	C–E♭–G♭–B𝄫	Cdim7 or C°7

Read the table as a decision sequence: identify the third, check the fifth, and then check the seventh. The third and fifth tell you the triad’s quality; the seventh completes the identification. The symbols, including the alternative half-diminished notation, are explained in Open Music Theory’s “Chord Symbols”.

These worked examples apply the interval rules above. Writing the three intervals beside the notes makes the reasoning easy to check.

D–F♯–A–C: D–F♯ is a major third, D–A is a perfect fifth, and D–C is a minor seventh. The first three notes form a major triad. A major triad plus a minor seventh gives D dominant seventh: D7.

A–C–E–G: A–C is a minor third, A–E is a perfect fifth, and A–G is a minor seventh. The triad is minor, and the seventh is minor, giving A minor seventh: Am7.

F–A–C–E: F–A is a major third, F–C is a perfect fifth, and F–E is a major seventh. This is F major seventh: Fmaj7.

F♯–A–C–E: F♯–A spans three semitones, F♯–C spans six, and F♯–E spans ten. Those intervals are m3, d5, and m7, giving F♯ half-diminished seventh: F♯m7♭5.

A useful check is to read your symbol backward and reconstruct the notes. For F♯m7♭5, start with F♯, add its minor third A and perfect fifth C♯, lower that fifth to C, and add its minor seventh E. You recover the original four notes.

C7 and Cmaj7 differ in their sevenths. In standard chord-symbol notation, an unqualified 7 indicates a minor seventh; maj7 specifies a major seventh. Thus C7 contains B♭, while Cmaj7 contains B. Both have the same major triad, C–E–G. See the defaults and symbol table in “Chord Symbols”.

Half-diminished and fully diminished chords also differ in their sevenths. Both contain a diminished triad. The half-diminished version adds a minor seventh, while the fully diminished version adds a diminished seventh. These are separate qualities in “Introduction to Seventh Chords”.

Compare B–D–F–A with B–D–F–A♭. Both begin with the diminished triad B–D–F. B–A is a minor seventh, so the first chord is Bm7♭5. B–A♭ is a diminished seventh, so the second is Bdim7.

The Cdim7 example requires B𝄫, meaning B double-flat. C–B♭ is already a minor seventh; lowering it one more semitone produces C–B𝄫, a diminished seventh. This applies the rule that a diminished interval is one semitone smaller than its minor or perfect counterpart, explained in “Augmented and Diminished Intervals”.

Once you know the root and quality, check the actual lowest note. If it differs from the root, a slash followed by that note specifies the bass. This notation is explained in Open Music Theory’s section on bass notes.

For example, take E–G–B–C with E as the lowest sounding note. Rearranging for analysis gives C–E–G–B, identifying Cmaj7. Restoring the bass information gives Cmaj7/E. The E after the slash tells the player which note belongs at the bottom.

This extra step prevents a common naming error: assuming the lowest sounding note must be the root. First identify the chord from its organized members, then describe its bass.

The five common qualities are a starting point. Other combinations exist, including minor-major seventh and augmented seventh chords, as “Chord Symbols” notes. If your intervals do not match the table, check the note spelling and measurements before choosing a name.

For example, C–E♭–G–B has a minor triad and a major seventh. Its symbol is Cm(maj7). Calling it Cm7 would change B to B♭; calling it Cmaj7 would change E♭ to E. Keeping the triad and seventh as separate findings preserves the actual notes.

When naming your next seventh chord, write the root, record the root-to-third and root-to-fifth intervals, and identify the root-to-seventh interval. Match that structure to a quality, write the symbol, and add a slash bass if needed. Finally, reconstruct the four notes from your answer to check that the name describes the chord you started with.

• Triads and seventh chords — Open Music Theory
• Chord Symbols — Open Music Theory
• Introduction to Seventh Chords — Music Theory for the 21st-Century Classroom
• How to Identify Perfect, Major, and Minor Intervals — Music Theory for the 21st-Century Classroom
• Augmented and Diminished Intervals — Music Theory for the 21st-Century Classroom