An interval is the distance in pitch between two notes. Every melody, chord, and scale you've ever heard is built from intervals — they're the atoms of music theory.
Half Steps and Whole Steps
The smallest interval in Western music is a half step (also called a semitone). On a piano, it's the distance from any key to the immediately adjacent key — white or black. On a guitar, it's one fret.
A whole step is two half steps — two frets on a guitar, or two adjacent keys skipping one in between on piano.
Interval Names
Intervals are named by the number of letter names they span and a quality (perfect, major, minor, diminished, augmented).
| Name | Half Steps | Example |
|---|---|---|
| Perfect Unison | 0 | C to C |
| Minor 2nd | 1 | C to D♭ |
| Major 2nd | 2 | C to D |
| Minor 3rd | 3 | C to E♭ |
| Major 3rd | 4 | C to E |
| Perfect 4th | 5 | C to F |
| Tritone | 6 | C to F# |
| Perfect 5th | 7 | C to G |
| Minor 6th | 8 | C to A♭ |
| Major 6th | 9 | C to A |
| Minor 7th | 10 | C to B♭ |
| Major 7th | 11 | C to B |
| Perfect Octave | 12 | C to C (higher) |
Quality
The quality of an interval describes its exact size:
- Perfect — applies to unisons, 4ths, 5ths, and octaves. These intervals sound stable and open.
- Major / Minor — applies to 2nds, 3rds, 6ths, and 7ths. Major is one half step wider than minor.
- Diminished / Augmented — a perfect or minor interval reduced by a half step is diminished; a perfect or major interval expanded by a half step is augmented.
Consonance and Dissonance
Some intervals sound stable and resolved — these are called consonant. Others create tension and want to move — these are dissonant.
- Consonant: perfect unison, major/minor 3rds, perfect 4th and 5th, major/minor 6ths, octave
- Dissonant: minor 2nd, major 7th, tritone (the most tense interval of all)
Dissonance isn't bad — it's what gives music motion. The tension of a dissonant interval resolving to a consonant one is one of the core engines of Western harmony.
Melodic vs Harmonic Intervals
When two notes are played one after the other, the interval is melodic. When they're played at the same time, it's harmonic. Chords are built entirely from harmonic intervals stacked on top of each other.
Why Intervals Matter for Songwriting
Once you can hear intervals, you can figure out melodies by ear, understand why chords have the emotional quality they do, and make intentional choices about tension and resolution in your music. The tritone creates dread; the major 6th sounds bright and open; the minor 3rd is bittersweet. These aren't accidents — they're the distances between the notes.