Music Intervals Complete Guide: From Unison to Octave
Published February 27, 2026
Master every musical interval from unison to octave. Learn to identify, build, and hear intervals by their unique sound character. Includes distance calculations, inverted intervals, and ear training tips.
Key Takeaways
- Intervals are distances between notes, measured in semitones.
- Perfect intervals: unison, 4th, 5th, octave. They sound pure and stable.
- Major intervals lower by one semitone become minor. The 3rd is the most important interval for chord quality.
- The tritone (6 semitones) is the most dissonant interval and drives dominant chord resolution.
- Associate each interval with a familiar song to train your ear.
What Is a Musical Interval?
A musical interval is the distance between two notes, measured in semitones (half steps). Intervals are the building blocks of melody, harmony, chords, and scales. Every relationship between two notes is an interval.
There are two ways to experience intervals: melodic (the two notes played one after another, like a melody) and harmonic (the two notes played simultaneously, like a chord).
Intervals have two properties: size (how many letter names apart) and quality (major, minor, perfect, augmented, or diminished). Together these fully describe any interval.
The Intervals of the Major Scale
Starting from the root of any major scale, each scale degree creates a specific interval:
Root to 1st: Unison (Perfect 1st) — 0 semitones. Same note.
Root to 2nd: Major 2nd — 2 semitones. 'Happy Birthday' opening.
Root to 3rd: Major 3rd — 4 semitones. 'When the Saints Go Marching In'. Bright, happy.
Root to 4th: Perfect 4th — 5 semitones. 'Here Comes the Bride'. Open, strong.
Root to 5th: Perfect 5th — 7 semitones. 'Star Wars' theme. Powerful, stable.
Root to 6th: Major 6th — 9 semitones. 'My Bonnie Lies Over the Ocean'. Warm, sweet.
Root to 7th: Major 7th — 11 semitones. 'Take On a' (first two notes). Bright, jazzy tension.
Root to 8th: Perfect Octave — 12 semitones. 'Somewhere Over the Rainbow'. Complete.
Perfect vs Major/Minor Intervals
Perfect intervals: Unison, 4th, 5th, and Octave. These intervals sound pure and consonant. When inverted (flipped upside down), a perfect interval remains perfect. They are the most stable intervals in music.
Major intervals: 2nd, 3rd, 6th, and 7th. When lowered by one semitone they become minor intervals. Major sounds bright; minor sounds dark.
Diminished intervals: Any perfect or major interval lowered by two semitones (or minor by one). The diminished 5th (tritone) is the most dissonant interval.
Augmented intervals: Any perfect or minor interval raised by two semitones (or major by one). The augmented 4th is also a tritone. Augmented intervals sound tense and unstable.
Inverted Intervals
An inverted interval flips the bottom note to the top. When you invert, the size changes (they add up to 9) and the quality changes (perfect stays perfect, major becomes minor, diminished becomes augmented).
Examples: Unison inverts to octave (1+8=9, both perfect). Major 3rd inverts to minor 6th (3+6=9, major→minor). Perfect 5th inverts to perfect 4th (5+4=9, perfect→perfect). Diminished 5th inverts to augmented 4th.
This is useful because if you can hear a major 3rd ascending, you can identify a minor 6th descending by the same two notes.
Practice Exercises
- 1Play the C major scale. After each note, sing or play the interval from C to that note. Name the interval as you go: unison, M2, M3, P4, P5, M6, M7, octave.
- 2Listen to the opening two notes of these songs and name the interval: 'Here Comes the Bride' (P4), 'Star Wars' (P5), 'Jaws' (m2), 'Somewhere Over the Rainbow' (P8).
- 3Pick a root note and build every interval above it: m2, M2, m3, M3, P4, tritone, P5, m6, M6, m7, M7, octave. Play each and name the semitone count.
Common Mistakes
- Confusing major and minor intervals. Major = 4 semitones for 3rds. Minor = 3 semitones for 3rds. The difference of one semitone changes the entire character.
- Thinking perfect intervals can become major or minor. Perfect intervals (4th, 5th, octave) are always perfect, never major or minor.
- Counting letter names incorrectly. An interval of a 3rd means three letter names (C to E: C-D-E = 3 letters). The quality (major/minor) is separate from the size number.
Frequently Asked Questions
How many semitones are in an octave?
There are 12 semitones in an octave. An octave doubles the frequency of the starting note (e.g., A4 = 440 Hz, A5 = 880 Hz).
What is a tritone?
A tritone is an interval of 6 semitones, exactly halfway through the octave. It can be called a diminished 5th or augmented 4th. It is the most dissonant interval in Western music and is the key component of the dominant 7th chord.
How do I practice interval ear training?
Associate each interval with a well-known song: Unison = 'Here Comes the Bride' (4th), 'Star Wars' (5th), 'My Bonnie' (6th), 'Somewhere Over the Rainbow' (octave). Listen to the interval, identify the song reference, then name the interval.
What is the difference between consonant and dissonant intervals?
Consonant intervals sound stable and pleasing (unison, 3rds, 5ths, 6ths, octave). Dissonant intervals sound tense and unstable (2nds, 7ths, tritone). Music creates tension by using dissonance and resolves it with consonance.