Intervals
The distance between two notes — how it is counted, what it is called, and why the spelling is not a choice.
C → E
Major third (M3)
C · D · E — 3 letters, so it is a third. 4 semitones across, which makes that third major.
Major third — 4 semitones
An is the distance between two notes, and its name has two halves that are measured in different ways.
The number comes from the letters, counted inclusively: C up to E is C, D, E — three letters, so a third. That is why the same-sounding note is a "first" rather than a zero, and why two thirds stacked make a fifth, not a sixth.
The quality — major, minor, perfect — comes from the exact size in . Both thirds cover three letters; the major one is four semitones and the minor one is three. On the staff they sit on the same line or space and differ only by an , which is exactly what makes them easy to confuse and worth practising here.
Fourths, fifths, octaves and unisons are called perfect rather than major or minor. It is a historical name for the intervals whose two notes share the simplest frequency ratios — nothing about them is more correct than a third.
One rule the tool never breaks: a third above B is some kind of D, because D is the letter three away from B. B up a major third is D♯, never E♭. Same sound, different note — and only one of them can be read.
About this tool
An interval is counted in letter names, not in semitones — C to E is a third because C, D, E is three letters, and it stays a third whatever accidentals arrive. Semitones then decide the quality: major, minor, perfect, diminished or augmented.
That distinction is where most confusion about intervals lives, and it is why an augmented second and a minor third sound identical and are not the same interval. Choose any two notes here and both halves of the answer are shown together, with the sound to go with them.
How to use it
- Choose a lower note and an upper note.
- Read the number and the quality, and why each is what it is.
- Hear it played together and one note after the other.
Questions
- How do I count an interval?
- Count the letter names inclusively, starting at one for the lower note. C up to G is C-D-E-F-G, so a fifth. Then the accidentals tell you whether it is perfect, diminished or augmented.
- What is the difference between an augmented second and a minor third?
- Three semitones each, so they sound the same. They are spelled differently and behave differently — the augmented second is what gives harmonic minor its distinctive step, and writing it as a minor third breaks the scale.
- Which intervals are perfect and which are major or minor?
- Unisons, fourths, fifths and octaves are perfect. Seconds, thirds, sixths and sevenths are major or minor. Any of them can be diminished or augmented.