Musical Intervals: Types, Qualities and Inversions
Discover how musical intervals are formed, named and transformed. From major and minor thirds to perfect octaves, explore interval qualities, inversions and their role in harmony through clear musical examples.
An interval is the distance between two notes. Learning to name intervals helps you read melodies, understand chords and recognise the sounds that give harmony its character.
This guide begins with the intervals inside an octave, explains how accidentals change their quality, and finishes with a simple way to invert any interval. Each musical example is on a single treble-clef staff, with interval names printed above the measures.
How many letter names? This gives its number (second, third, fifth…). How many semitones? This determines its quality (major, minor, perfect, augmented or diminished).
Counting intervals
Count both the starting and ending letter names. C–D is a second (C, D); C–E is a third (C, D, E). Sharps and flats do not change this letter-name count.
A melodic interval is heard when the notes occur one after another; a harmonic interval is heard when they sound together. The distance is named in the same way in both cases.
Whole tones, semitones and interval quality
A semitone is the smallest step in the usual 12-note chromatic system; a whole tone equals two semitones. On the piano, C–C♯ is one semitone, and C–D is two semitones.
The intervals of a major scale are a useful starting point. From C, the seconds, thirds, sixths and sevenths are major; the unison, fourth, fifth and octave are perfect.
| Interval | Example | Semitones | Whole tones |
|---|---|---|---|
| Perfect unison | C–C | 0 | 0 |
| Major second | C–D | 2 | 1 |
| Major third | C–E | 4 | 2 |
| Perfect fourth | C–F | 5 | 2½ |
| Perfect fifth | C–G | 7 | 3½ |
| Major sixth | C–A | 9 | 4½ |
| Major seventh | C–B | 11 | 5½ |
| Perfect octave | C–C (upper octave) | 12 | 6 |
How qualities change
For a major interval, lowering the upper note by one semitone produces a minor interval. One semitone above major is augmented; one semitone below minor is diminished. Perfect intervals have no major/minor forms: raising a perfect interval by one semitone makes it augmented, and lowering it by one makes it diminished.
The table below gives the semitone distances for every standard quality within an octave. A dash means that quality is not used for that interval number.
| Number | Diminished | Minor | Perfect | Major | Augmented |
|---|---|---|---|---|---|
| Unison | — | — | 0 | — | 1 |
| Second | 0 | 1 | — | 2 | 3 |
| Third | 2 | 3 | — | 4 | 5 |
| Fourth | 4 | — | 5 | — | 6 |
| Fifth | 6 | — | 7 | — | 8 |
| Sixth | 7 | 8 | — | 9 | 10 |
| Seventh | 9 | 10 | — | 11 | 12 |
| Octave | 11 | — | 12 | — | 13 |
Spelling matters: C–D♭ and C–C♯ sound the same on a standard piano, but the first is a minor second and the second is an augmented unison. Likewise, C–F♯ is an augmented fourth, whereas C–G♭ is a diminished fifth.
The five qualities in notation
The following examples reconstruct the source's interval-quality chart. All examples begin on C and show ascending notes. The perfect-family rows omit major and minor, while the major-family rows omit perfect.
To practise this interval on the keyboard, try the Major Scale Thirds exercises on Qlavist.
For octave practice, explore the ascending octave exercise on Qlavist.
Changing the lower note also changes the interval
Not every alteration must be made to the upper note. If the upper note stays at A, raising the lower C to C♯ reduces a major sixth to a minor sixth; lowering it to C♭ expands the sixth to an augmented sixth; raising it to C𝄪 contracts it to a diminished sixth. The letter names still span a sixth.
Beyond the octave: compound intervals
When notes are more than an octave apart, we continue counting: a ninth is an octave plus a second, a tenth an octave plus a third, and so on. Their quality follows the corresponding simple interval, but their actual semitone distance includes the extra octave.
| Interval | Equivalent | Semitones |
|---|---|---|
| 9th | Octave + major 2nd | 14 |
| 10th | Octave + major 3rd | 16 |
| 11th | Octave + perfect 4th | 17 |
| 12th | Octave + perfect 5th | 19 |
| 13th | Octave + major 6th | 21 |
| 14th | Octave + major 7th | 23 |
| 15th | Two octaves | 24 |
Inverting intervals
To invert an interval, move its lower note up an octave or its upper note down an octave. The pitches exchange their relative positions. For example, C–E is a major third; moving C above E produces E–C, a minor sixth.
New interval number = 9 − original interval number.
New semitone distance = 12 − original semitone distance.
These formulas apply to simple ascending intervals contained within one octave, including unison and octave as complementary cases. For larger intervals, first reduce them to their simple equivalent.
| Original | Inversion | Example |
|---|---|---|
| Unison (1) | Octave (8) | C–C → C–C (octave apart) |
| Second (2) | Seventh (7) | C–D → D–C |
| Third (3) | Sixth (6) | C–E → E–C |
| Fourth (4) | Fifth (5) | C–F → F–C |
| Fifth (5) | Fourth (4) | C–G → G–C |
| Sixth (6) | Third (3) | C–A → A–C |
| Seventh (7) | Second (2) | C–B → B–C |
| Octave (8) | Unison (1) | C–C → C–C (same pitch) |
Notice that major changes to minor, augmented changes to diminished, and perfect stays perfect. The inversion of a major third (4 semitones) is a minor sixth (8 semitones): 4 + 8 = 12.
Inversion changes quality too
Here are six examples: a major third becoming a minor sixth, a minor third becoming a major sixth, an augmented fourth becoming a diminished fifth, and their inverse relationships.
One more useful example: a diminished seventh spans 9 semitones (C–B𝄫). Its inversion is an augmented second spanning 3 semitones (B𝄫–C). Conversely, an augmented fifth of 8 semitones inverts to a diminished fourth of 4 semitones.
Consonance and dissonance
Traditional harmony groups unisons, octaves and perfect fifths among the most stable-sounding intervals; thirds and sixths are also commonly treated as consonant. Seconds, sevenths and many augmented or diminished intervals tend to create more tension. A perfect fourth can function differently depending on the musical context, especially when heard above the bass.
These are descriptions of how intervals behave in many classical styles, not universal rules about what sounds beautiful. Different musical traditions and styles use tension and stability in their own ways.
Try it at the piano
For more guided practice, explore the Practice Paths on Qlavist.
- Play C–E and name the interval before you look at the table. Lower E to E♭: what changed?
- Play C–F♯ and C–G♭. Listen: same piano keys, different interval spellings.
- Play C–A, then move C up an octave. Say the inverted interval's name and count its semitones.
- Choose any starting note and build a major third, a minor sixth and a perfect fifth without relying on C.
Count letters to find the interval number; count semitones to identify its quality. To invert a simple interval, subtract its number from 9 and its semitones from 12.