I've read few articles about it, but none of them seem to help me with this problem.

Let's say we have a song in certain key - which harmonica should I choose? Let me give you an example, we have a song "She caught the Katy":

I have tried many keys (C, E, F - that's all I have) and none of them fit. Any Ideas?

And is there any general method of choosing harmonica key basing on key of the song?

Thanks for any help!

3 Answers 3


It is indeed in Bb. Which means to play in a bluesy way, you have to suck more than blow. Go up a fourth and there's your answer. An Eb harp, which, when sucked, will give notes akin to Bb9.

To play an ordinary melody, you'll use Bb, the key it's in.

To play blues, you need to be a perfect fifth above/ perfect fourth below your existing harp key. So, blues in A - harp in F_D.On your C harp, play G blues, on your E harp, play B blues, and on the F harp, C blues'll sound good.

If you're trying this number with a band, get them to do it in C,as it's closest to Bb, and use the F harp.Or buy others - you will eventually need the full set to jam in any key !

  • 2
    This is often called playing "cross harp". Apr 7, 2015 at 13:43

If I'm hearing correctly, the band in the recording is playing in Bb. To give it a bluesy sound, you will want to use your Eb harp.

You want to learn about the Circle of Fifths and playing in the different "positions" on your harp. In particular, first position or "straight harp" is playing music in the key of the harmonica. Second position or "cross harp" or "blues harp" is playing a perfect fifth above the key of the harp. That is, on your C harp, play in G.

For the question I hear buried in this, which harp should I buy? The answer is, eventually all of them :-D Talk to your bandmates and determine the most common keys your songs are in and get the harps for those


The answers above so far cover songs in major scales. A major scale also has a relative minor. However there are some 20-30 popular scales, and far far more than that possible. In fact there are 332,640 possible scales of 7 semitones per key. [see calculation below]

At very best a 'correct' harmonica is going to give you a couple harmonious chords and one 7 semi-tone scale, which could even be Phrygian if you pick the right key and don't mind that the scale is not complete, but half an octave above and below the root.

That said, choosing the right harmonica for the job is a tedious task involving spread sheets in which both the song and types of harmonicas are laid out as intervals across cells, and then rows are duplicated 12 times and shifted over to determine which key of that type of harmonica has the most matching notes, or lacks wrong notes when blowing or drawing. Throwing in harmonicas like Oskars in harmonic minor scales will increase your chances at getting a closer match, but for any uncommon scale, it's always going to be a compromise unless the piece was composed for that harmonica to begin with. - Indeed, if you are going to seriously involve a harmonica in a song of any slightly uncommon scale, it's much easier and cheaper to have the guitars and piano play to you than to play to them.

Aside from that though, the art of harmonica is working around that, and learning how to weave in notes which are off key or out of scale. You can get that to sound intentional and great if you are accomplished at improvisational strategies, but it will assuredly significantly change the color of the song, and your band partners may not welcome that no matter how skillful it's done. Some people don't want phyrgian overtones in the mix.

[Root note = 12 possible notes :: x 11 possible notes to omit :: x 10 possible notes to omit :: x 9 possible notes to omit :: x 8 possible notes to omit :: x 7 possible notes to omit :: x 6 possible notes to omit = 3,991,680 possible total western scales or 332,640 7 semi-tone scales per key.]

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