I love blues and everytime I listen to harp (harmonica) on some Sonny Terry with Brownie McGhee for example, I really want to play Harp, the problem is how to know which Key, should I be based on the guitar scale ?

In this example : Jimi Hendrix - My Friend Harmonica is same scale played on guitar/bass ?

2 Answers 2


Playing blues on a harp, drawing is the way to go. Blowing on, say, a C harp will give you the notes of that chord - C. So the blues notes, mainly, give the chord a fourth away - G. So, for a song in G, you'd need a C harp.

To calculate what you need, know the guitar key, and count backwards 5, or more simply, forwards 4. As in, song's in A, use D. Song's in E, use A. Song's in G, need a C harp (as in the Hendrix song!).

All that's called cross harp. A lot of good players will resort to using two in a song - one in the actual key, one in cross key.

  • Why is that? Do harmonicas not have chromatic scales, but rather they only have diatonic scales in a key? (sorry for a newbie question, I am clueless when it comes to harmonicas) Commented Oct 29, 2019 at 22:54
  • @barrypicker Yep, the most common type of harmonica is a 10-hole diatonic harmonica that plays in one fixed key (with some chromatic notes accessible by bending). There are also chromatic harmonicas available that essentially combine two diatonic harmonicas tuned a half-step apart and give you a button to switch between them, kind of like a double French horn. Commented Oct 30, 2019 at 0:41

Generally, for blues, if guitar plays in C you would use an F harp. This is to get the Bb ("blue 7th"), otherwise known as Mixolydian mode. In general, you want the harp whose key is a perfect 4th above the key of the blues. So:

For a E blues, an A harp

For a D blues, a G harp

and so on.

  • You could also look at it the other way around. If you have an A harp, guitarist plays blues in E, etc. Guitarists shouldn't have a problem playing blues in any key. Commented Oct 29, 2019 at 10:34
  • 2
    @piiperi - true, guitarists can often play blues in any key - singers are a different kettle of fish. Decent harp players will have at least half a dozen keyed harps. Just owning an A harp severely restricts the numbers you can join in on. Unless you're the harp player at our local open mic - who thinks his will work in any number. Wrong!!
    – Tim
    Commented Oct 29, 2019 at 10:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.