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Ten holes, twenty reeds, and a clever layout
A diatonic harmonica has ten holes, and each hole has two reeds: one that sounds when you blow, one when you draw. That gives twenty basic notes, but the layout is not a simple scale. It follows Richter tuning, designed so that blowing gives chords and drawing gives melody, and understanding that layout is the key to the whole instrument.
The tool above charts every hole for any harmonica key. Pick a key and it shows the blow note, the draw note, the available bends, and the overblow or overdraw for each hole. Change the key and the whole chart transposes, because the pattern of intervals is the same on every harmonica.
Blow notes: the chords
On a C harmonica, the blow notes across the holes are C, E, G, C, E, G, C, E, G, C. Blow anywhere across several holes and you hear a C major chord, because every blow note belongs to it. That is no accident: the harmonica was designed as a chordal instrument, and blowing a chord is the easiest thing it does.
That chord layout also means the blow notes alone never give a full scale. Holes one to four blow C, E, G, C, skipping D and F. The missing notes live on the draw reeds, which is why harmonica playing constantly alternates breath direction.
Draw notes: the melody
The draw notes on a C harmonica are D, G, B, D, F, A, B, D, F, A. Together with the blow notes, holes one to four give a complete C major scale: C, D, E, F, G, A, B, C. That first octave is fully available without any bending, which is why beginners start there.
The upper holes work differently. Holes five to ten draw F, A, B, D, F, A, and the scale there needs bends to fill the gaps. The layout repeats in patterns but with twists, because the reeds must fit the physical limits of the instrument. Learning the chart hole by hole, rather than assuming a pattern, is what prevents confusion later.
Bends: the notes between the notes
A bend lowers a reed’s pitch by changing the shape of your mouth and throat, and it is how harmonica players reach the chromatic notes that Richter tuning leaves out. Draw bends live on holes one to six, with hole three offering three bends, and blow bends live on holes eight to ten. Hole seven does not bend at all.
Bends are also the soul of blues harmonica. Second position, or cross harp, plays a C harmonica in the key of G, and the draw bends on holes one to five become the blue notes of the scale. That is why a ten-dollar harmonica can sound so expressive: the bends are built into the design.
Overblows and overdraws
Overblows on holes one to six and overdraws on holes seven to ten sound one semitone above the draw note, and they complete the chromatic scale for advanced players. They need precise embouchure and a well-adjusted harmonica, and they are not a beginner technique. The chart lists them so you can see the full map, but treat them as a later goal, not a starting point.
Most players spend years on bends before overblows feel reliable. That is normal. The instrument rewards patience: a clean single note matters more than a forced overblow, and a well-played bend matters more than a shaky chromatic run.
Choosing a harmonica key
Harmonicas come in every key, and the choice depends on the music. A C harmonica suits learning and folk music. Blues players in a band often carry several keys and pick the one a fourth above the song’s key for cross harp. Use the tool to compare keys: pick the song’s key, find the harmonica whose chart puts the melody’s notes in comfortable holes, and let the layout decide.
Whatever key you play, learn the chart for that harmonica. Knowing which holes blow and draw, and where the bends live, turns the harmonica from a mysterious toy into an instrument you can play deliberately.
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