Music Intervals Explained

What Is an Interval?

An interval is the distance in pitch between two notes. Play C, then play G above it, and the gap between them is an interval—in this case a perfect fifth.

Intervals matter because they're the atoms of everything else in music theory. Scales are chains of intervals. Chords are stacks of intervals. Melodies are sequences of intervals. When you can name and hear intervals, chords and scales become intelligible structures rather than lists to memorize.

Intervals take two forms depending on how the notes are played. If the notes sound one after the other, it's a melodic interval. If they sound at the same time, it's a harmonic interval. The name is identical either way—C to E is a major third whether it's sung as a melody or struck as a chord.

1 Every Interval Has a Two-Part Name

An interval's full name has two parts, and each part answers a different question:

• The number (second, third, fourth, fifth…) — how many letter names the interval spans on the staff.
• The quality (perfect, major, minor, augmented, diminished) — the exact size in semitones.

You need both. "A third" isn't a complete name, because C to E and C to E♭ are both thirds on the staff—but they're different sizes and they sound completely different. C to E is a major third; C to E♭ is a minor third. The number gets you to the neighborhood; the quality gives you the exact address.

Two questions, two answers. Number: how far apart do the notes look on the staff? (Count letter names.) Quality: how far apart do the notes sound? (Count semitones.)

2 Count the Number — Including Both Endpoints

To find an interval's number, count every letter name from the bottom note to the top note, counting both notes themselves.

From C up to E: C (1), D (2), E (3). Three letter names, so it's a third.

From F up to C: F (1), G (2), A (3), B (4), C (5). Five letter names, so it's a fifth.

The off-by-one trap. The single most common interval mistake: counting the steps between the notes instead of the letter names. C to E is two steps of travel, so students want to call it a "second." But interval numbers count letter names, both endpoints included—C, D, E is three names, so it's a third. Think of it like floors in a building: walking from the 1st floor to the 3rd floor puts you on the third floor, even though you only climbed two flights.

Two useful edge cases: two notes with the same letter name and pitch form a unison (an interval of 1), and eight letter names—C up to the next C—form an octave (from the Latin for "eighth").

One more thing worth noticing: accidentals never change the number. C to E, C to E♭, and C♯ to E are all thirds, because they all span three letter names. Accidentals only affect the quality—which is the next step.

3 Add the Quality

The quality pins down the exact size of the interval in semitones (half steps). The system looks intimidating at first, but it rests on one simple split:

• Unisons, 4ths, 5ths, and octaves get the quality perfect. These intervals sound unusually stable, open, and "hollow"—they were the first intervals medieval theorists accepted as consonant, which is where the name comes from. There's no such thing as a "major fifth."
• 2nds, 3rds, 6ths, and 7ths come in two everyday sizes: major (the larger) and minor (one semitone smaller). C to E is a major third (4 semitones); C to E♭ is a minor third (3 semitones).

Beyond those everyday sizes, two more qualities describe expansions and contractions:

• Augmented — one semitone larger than perfect or major. C to G♯ is an augmented fifth.
• Diminished — one semitone smaller than perfect or minor. C to G♭ is a diminished fifth.

The size ladder. For 2nds, 3rds, 6ths, 7ths: diminished → minor → major → augmented. For unisons, 4ths, 5ths, octaves: diminished → perfect → augmented. Each arrow is one semitone. Perfect intervals skip straight from diminished to perfect to augmented—no major or minor versions exist.

4 The Complete Interval Chart

Here is every interval within one octave, from smallest to largest, measured from C. The reference songs are famous melodies that open with that interval—an easy hook for your ear when you start training it.

There is no need to memorize all thirteen rows at once. Learn a handful at a time—the perfect intervals and the thirds are the best starting set—and let the songs do the remembering for you. Our interval reference songs page has a fuller list, including descending examples.

5 Interval Inversion: The Rule of Nine

Take any interval and move its bottom note up an octave (or its top note down an octave) so the two notes trade places. That's an inversion. C up to E is a major third; move the C up an octave and you get E up to C—a minor sixth.

Inversions follow two reliable rules:

• The rule of nine: an interval and its inversion always add up to 9. Thirds invert to sixths (3 + 6 = 9), seconds to sevenths, fourths to fifths, unisons to octaves.
• Quality flips: major ↔ minor, augmented ↔ diminished, and perfect stays perfect. A major third inverts to a minor sixth; an augmented fourth inverts to a diminished fifth; a perfect fifth inverts to a perfect fourth.

Why inversion matters. Inversion halves your workload. If you know C up to E is a major third, you instantly know E up to C is a minor sixth—no counting required. It's also everywhere in real music: chord inversions, invertible counterpoint, and figuring out descending intervals from ascending ones all lean on the rule of nine.

Why Spelling Matters: A4 vs. d5

C to F♯ and C to G♭ are the same six semitones—press the same two piano keys and you'll hear the identical sound. So why do they get different names?

Because the names describe function, not just distance. C to F♯ spans four letter names (C, D, E, F), so it's an augmented fourth; C to G♭ spans five (C, D, E, F, G), so it's a diminished fifth. And in real music, that spelling tells you where the notes want to go: an augmented fourth tends to expand outward to a sixth, while a diminished fifth tends to collapse inward to a third. Same sound, opposite behavior. Intervals like these—identical in sound, different in spelling—are called enharmonic equivalents, and choosing the right spelling is what makes your notation readable to other musicians.

Compound Intervals in Brief

Intervals larger than an octave are called compound intervals; each is a simple interval expanded by an octave. A ninth is a second plus an octave: C up to the D above the next C. A tenth is a third plus an octave; an eleventh is a fourth plus an octave; a thirteenth is a sixth plus an octave.

The quality carries over unchanged—a major ninth is just a major second an octave wider. You'll meet compound intervals constantly in chord symbols (C9, C11, C13), so it's worth knowing the pattern: subtract 7 to find the simple interval inside. A 9th contains a 2nd, an 11th contains a 4th, a 13th contains a 6th.

Practice free: Interval Flashcards →

The flashcards show two notes on the staff and check your answer instantly. Drill the ascending set first, then the descending set — the same skill, reading downward.

Related: identify intervals by ear · interval reference songs · interval ear training.