Today for PianoTV’s Halloween Week, we’re going to talk about the question “What is a diminished chord?”, especially the diminished 7th, because it’s a very dark, tense, dissonant chord.

The diminished triad

So first of all, let’s look at how to build a diminished triad – triad means three, so we’re building a diminished three-note chord.

A major triad would be notated like this:

1 – 3 – 5

And a minor triad would be notated like this:

1 – b3 – 5

So to interpret this with the example of a C major triad, since there are no naturally occurring sharps or flats in C major, the 1 – 3 – 5 formation would be C – E – G. C minor would look like C – Eb – G. From there, we can create a diminished triad.

The notation for a C diminished triad might look like this:

1 – b3 – b5

So with our C example, a C minor chord would be C – Eb – G, whereas a C diminished triad would be C – Eb – Gb.

How to build diminished triads on any note

To figure out a diminished triad starting on any note, all you have to do is pick a note, hop up three semitones to the next note, and then hop up 3 more semitones to the final note.

So say we start on an F. Find the F, then the next note is 3 semitones up – Ab – and the final note is 3 more semitones up – Cb (or B). It doesn’t matter where you start – you can build diminished thirds just by building groups of 3 semitones.

how a diminished triad is notated

Just a quick note on what that diminished chord might be notated as in your music, if you’re reading lead sheets or printing chords off the internet. Sometimes it’ll be as simple as “Cdim”, short for diminished, or it might say “Cm-5” or “Cmb5”, to indicate that it’s a minor chord with a lowered 5th.

What is a diminished chord – the diminished 7th

Now the diminished triad is all well and good, but you’re much more likely to come across its larger version, the diminished 7th. The diminished 7th is exactly the same as the diminished triad – you just add a 7th on top of it.

So a diminished 7th is this:

1 – b3 – b5 – bb7

Yes, that is a double flatted 7th. Figuring out a double flat is easy – it’s just what it sounds like. If you have Abb, you just go down two semitones – so an Abb is actually a G.

So let’s figure out C diminished 7th chord:

C – Eb – Gb – Bbb

Bbb is technically an A, which is a little easier to think about.

Find a diminished 7th chord on the keyboard

Now to figure out any diminished 7th chord on the keyboard, it’s actually very easy – your original diminished 7th triad is built on groups of 3 semitones. C to Eb is 3 semitones, and Eb to Gb is three semitones. To figure out the 7th note, you just have to go up 3 more semitones. So three semitones up from Gb is A (or, more correctly, Bbb).

So let’s pick a random letter and build a diminished 7th chord from it. How about Ab.

Our first letter is Ab, then up three semitones is Cb (B), and then three more semitones is D (Ebb), and then three more semitones is F (Gbb). That’s all there is to it!

There are only 3 diminished 7th chords

One thing you might notice is there are actually only three different configurations of diminished 7th chords. If I play a diminished 7th on C, I have the notes C – Eb – Gb – A. Now if I go and play a diminished 7th chord on Eb as the first note, it’ll look like Eb – Gb – A – C. It’s the same chord, just inverted.

So the three different configurations are here on C, on Db, and on D. Then they start repeating themselves.

how diminished 7th chords are notated
You might see diminished 7ths notated as chords like this:

Cdim7, or C*7 (imagine the asterisk is a circle). This is a really common chord in classical music, as well as jazz.

What is a diminished chord – music examples

And now for a couple examples of how a diminished 7th chord sounds like in context of a song snippet. Our first example is from Bach. It’s from his book “The Well-Tempered Clavier, Vol. 1”, and it’s the first piece in C major.

Check out today’s video to follow along the sheet music and see exactly where the diminished 7th chords are – measures 12 and 14 specifically (there are many more, but those are the ones in the first 30 seconds of the piece).

The final bars of Beethoven’s Appassionata sonata, in the second movement (Andante) have some intense diminished chords. It ends on a very dark, disturbed note – again, see the video for a listening example with music.


So hopefully you feel armed and ready to tackle any diminished chord, or diminished 7th, that comes your way. In the next video, we’re going to learn a piece that uses it, and it’s very creepy and totally appropriate for Halloween.



  1. […] done several chord videos in the past, like how to play major and minor chords, diminished chords, all kinds of 7 chords, and inverting chords. Definitely check out the links if you need a […]

  2. […] the chord videos we’ve done – major and minor, 7 chords, diminished chords and suspended chords – can be found by following the links, so if there’s anything you’re […]