Chord Theory

A Diminished 7th chord is a dissonant or unstable chord and generally needs resolution. Guitarists often play the diminished 7 or dim7 (4-note chord) instead of the diminished triad (dim) or 3 note chord.
  • dim7 chords are 4 note chords consisting of 3 minor 3rds above the root or tonic, therefore having a root, a minor 3rd, a diminished 5th and a diminished 7th.
  • The chord formula for a dim7 is 1 - ♭3 - ♭5 - ♭♭7(6)
  • The symbols for a diminished 7th chord are, dim7 or º7
  • The featured song for this session using dim7 chords is 'Love is a Losing Game' written and performed by Amy Winehouse... some excellent backing by the guitarist and bass player.
  • For Country Music Fans we have another featured song by Patsy Cline called Crazy. It has a great melody with some very nice diminished 7 chords and a vast array of barre chords. Every learning guitarist will enjoy playing this one.
Example... Calculating C diminished 7th... Cdim7 or Cº7
  • Diminished 7th chords consist of the 1st, ♭ 3rd, ♭5th and ♭♭7th notes of a Major Scale
  • Remember that a minor third is equal to 3 half steps or 3 semitones. If we move a minor third upwards from C, we get E♭...(C - C# - D - E♭). If we move another minor 3rd upwards from E♭, we get G♭... (E♭- E - F - G♭). If we move another minor 3rd upwards from G♭, we get B♭♭... (G♭ - G - A♭ - B♭♭)... B♭♭ is actually an A. We call it a B♭♭ because it is the 7th note of the C diatonic scale which is B.
  • Remember that all chords are based around the major scale of that chord, therefore C chords are built from the C major scale which consists of no sharps or flats. The scale reads as follows: C - D - E - F - G - A - B - C
  • Formula for a dim7 chord = 1 - ♭3 - ♭5 - ♭♭7
  • Substitute the notes into the formula: 1=C, ♭3=E♭, ♭5=G♭, ♭♭7=♭♭B (A)
  • Cdim7 reads as follows: C - ♭ E - ♭G - B♭♭(A)
Diminished 7th Chord Table
dim 7 A A# B♭ B C C# D♭ D  
Root A A# B♭ B C C# D♭ D  
♭3rd C C# D♭ D E♭ E F♭ (E) F  
♭5th E♭ E F♭ (E) F G♭ G A♭♭ (G) A♭  
♭♭7th G♭ G A♭♭ (G) A♭ B♭♭ (A) B♭ C♭♭ (B♭) C♭ (B)  
dim 7 D# E♭ E F F# G♭ G G# A♭
Root D# E♭ E F F# G♭ G G# A♭
♭3rd F# G♭ G A♭ A B♭♭ (A) B♭ B C♭ (B)
♭5th A B♭♭ (A) B♭ C♭ (B) C D♭♭ (C) D♭ D E♭♭ (D)
♭♭7th C D♭♭ (C) D♭ E♭♭ (D♭) E♭ F♭♭ (E♭) F♭ (E) F G♭♭ (F)

Diminished 7th Chords - Right Handers

Please note that all chord charts indicate different shapes in different fret positions rather than set fret positions. Generally, there are 3 different dim7 shapes and each one can be played in 4 different positions. Let's say that you like playing the third shape, and you are looking for a Cdim7 chord... as long as the shape stays intact and any one of your 4 fingers lands on a C note, you are playing a Cdim7 chord. The same applies to the other shapes.

This also means that the same Cdim7 chord which contains the notes C-Eb-Gb-A, can also be an Ebdim7, Gbdim7 and Adim7 chord. This gives us heaps of choices. If you want to play Cdim7 and want to lead with a C note, you would play the 1st shape with the arrow representing the 11th fret, the second shape - arrow representing the 3rd fret, and the third shape with the arrow representing the 8th fret. You may want a sound that is higher up the fretboard or lower down or somewhere in between... so many flavors to choose from!