Sizing Up Intervals to Play the Harmonica
Very few people have the ability to name what note they’re hearing. That ability is called absolute pitch or perfect pitch. But most harmonica players and musicians have a much more useful skill: They can hear and describe the relationships among notes using intervals. Those relationships create structure in scales, melodies, chords, and harmonies. When you know the structures, the specific notes are just details that you can figure out.
Counting out the size of an interval
An interval is the distance between two pitches. You measure the size of an interval by starting with the letter name of the first pitch and then counting up or down the scale to the second pitch. You already know two intervals — the unison, where two people sing the same note, and the octave, where they sing two pitches that are eight notes apart in the scale.
You can memorize all the intervals, but it’s easy to figure out any interval just by counting:

Choose one of the notes and give it the number 1.

Count up or down to the other note. The resulting number gives you the interval.

Seconds: Counting up from A to B (1, 2) gives you a second. So does B to C, C to D, and so on.

Thirds: Count up 1, 2, 3.

Fourths: Count up 1, 2, 3, 4.

Fifths: Count up 1, 2, 3, 4, 5.

Sixths: Count up 1, 2, 3, 4, 5, 6.

Sevenths: Count up 1, 2, 3, 4, 5, 6, 7.


If you’re starting with a specific note name and want to know what note would be, say, a fifth above it, just start on the note name you know, count up 5, and you’ll arrive at the other note name.
Here are all the intervals up to an octave counting up from any note name.
1  2nd  3rd  4th  5th  6th  7th  Octave 

A  B  C  D  E  F  G  A 
B  C  D  E  F  G  A  B 
C  D  E  F  G  A  B  C 
D  E  F  G  A  B  C  D 
E  F  G  A  B  C  D  E 
F  G  A  B  C  D  E  F 
G  A  B  C  D  E  F  G 
When you’re figuring out the size of an interval, only letter names matter. Sharps and flats have no effect. However, flats and sharps do affect the quality of intervals.
Determining the quality of an interval
While every interval has a size counted in letter names, it also has a quality measured in semitones. For instance, the second between C and D is a whole tone. However, the second between E and F is only a semitone. So one of those seconds is bigger and one is smaller. The bigger second is called a major second and the smaller second is called a minor second.
All intervals have at least two qualities, even the octave. Here are the most widely used qualities of intervals.
Interval Size  Interval Quality  Number of Semitones 

Second  Minor  1 
Second  Major  2 
Third  Minor  3 
Third  Major  4 
Fourth  Perfect  5 
Fourth  Augmented  6 
Fifth  Diminished  6 
Fifth  Perfect  7 
Fifth  Augmented  8 
Sixth  Minor  8 
Sixth  Major  9 
Seventh  Minor  10 
Seventh  Major  11 
Octave  Perfect  12 