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How does the circle of fifths work?

Updated: Jun 21

In today's harmonica lesson I'll be teaching you about the circle of fifths. It's a really useful tool for playing in different positions and knowing which key of harmonica you need. It will also help you understand a little bit more about music theory and keys.

You can download the free summary on circle of fifths by clicking here: Free Circle Of Fifths Summary Guide.

What is the circle of fifths?

The circle of fifths is a great tool for understanding various aspects of music. It helps musicians of all instruments, but has some particular applications for harmonica players. I’ll go through a bit of both.

How do we begin to understand the circle of fifths?

The diagram is built around intervals of a fifth (as the name suggests). This means that the distance from one letter to the next is five notes up the scale. For example, C to G (C > D > E > F > G). If we apply this interval to each scale around the circle, we can build a full circle of notes.

Circle of fifths diagram with 'fifth' interval

Working out V (dominant) chords

For blues or other popular music it can be useful to know what chord the V chord is. To work this out we can just jump one space clockwise around the circle from the key of the song and we’ll have the V chord. This is really useful in building a better understanding of which chords we’re playing over.

Adding key signatures

We can add a ‘key signature’ to the circle of fifths. This tells us how many sharps and flats are used in a given key. (This isn’t crucial for harmonica players but is useful for lots of other instruments).

Alternatively we can count around the circle to find out how many sharps or flats a key will have. If we go clockwise from C, we add a sharp note every time. If we go anti-clockwise from C, we add a flat note every time.

Circle of fifths with key signatures added


The keys that sit closest together around the circle are like siblings. If we travel further away then we get cousins, and further still we get only acquaintances and then virtual strangers. Closer keys will go together safely and easily. Keys that are at opposite sides of the circle will not go together easily; this doesn’t mean they can’t be put together but it will have a certain jarring effect.

Relative minor keys

Each major key has a relative minor key: a minor key which contains the same notes as its relative major. For example, C major and A minor contain the same notes. This is often written on the circle of fifths to help develop an understanding of the connection between major and minor.

Circle of fifths with relative minor keys

Working out positions: from the key of the harmonica

For harmonica players specifically, the circle of fifths is an absolutely fantastic tool for working out any position on any key of harmonica. For second position, we just jump one letter clockwise from our key of harp to work out what key we’ll be playing in (e.g. key of harp is C, key of song is G). For third position, we just jump another letter (e.g. key of harp is C, key of song is D). We can do this with any position for any key. We would usually need a big diagram to write out all those keys but the circle of fifths condenses that knowledge extremely efficiently.

Circle of fifths for second position harmonica playing
Circle of fifths for 3rd position harmonica playing
Circle of fifths with harmonica positions for C harp

Working out positions: from the key of the song

Often we get told the key of the song and we have to decide what harmonica to play. We can go from the key of the song to the key of the harmonica by going anti-clockwise: the exact opposite of what we did above. E.g. for second position, if the key of song is G, the key of harp is C.

Circle of fifths for working out harmonica key from key of song

Thanks for taking this lesson. I hope you enjoyed it!

Want more? I have a FULL music theory for harmonica course.

You can access this via my online school or a stand-alone course.

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