What is a musical interval? Explained with examples

Half steps and whole steps: the units of measurement

In Western music, the smallest distance between two notes is the half step, also called a semitone. On the piano, it is the distance from one key to the next, whether white or black; on guitar, from one fret to the next. Two half steps make a whole step.

Look at the keyboard: there is no black key between E and F, or between B and C. That detail explains much of music theory, including the structure of major and minor scales.

How to name an interval in two steps

1. Number: count note names from the first to the last, including both. From C to G: C, D, E, F, G. That is five, so it is a fifth. Sharps and flats do not change the number: C–E♭ is still a third.
2. Quality: count the half steps and compare them with the chart below. C–E♭ has three half steps, so it is a minor third; C–E has four, so it is a major third.

A few examples to practice the method:

• D–F: three note names and 3 half steps, a minor third.
• F–A: three note names and 4 half steps, a major third.
• E–B: five note names and 7 half steps, a perfect fifth.
• B–F: five note names and 6 half steps, a diminished fifth.
• C–F♯: four note names and 6 half steps, an augmented fourth.

An interval is melodic when the notes sound one after another, and harmonic when they sound together. A melodic interval can also be ascending or descending.

Types of intervals

Intervals are classified by their number (from unison to octave), quality (major, minor, perfect, augmented, or diminished), how the notes sound (melodic or harmonic), size (simple or compound), and consonance or dissonance.

Consonant intervals include the unison, octave, perfect fifth, and major and minor thirds and sixths. Seconds, sevenths, and the tritone are dissonant. The perfect fourth depends on the context: on its own, it sounds open and stable, but above the bass in a chord it can sound as though it is waiting to resolve.

Interval chart: major, minor and perfect

The rules for changing quality are simple. A major interval reduced by a half step becomes minor; a minor interval reduced by a half step becomes diminished; a major interval increased by a half step becomes augmented. Perfect intervals become augmented or diminished directly when increased or reduced by a half step.

A two-whole-step interval: the major third

An interval of two whole steps is a major third. Two whole steps add up to 4 half steps, the size of a major third, for example from C to E (C–D is one whole step and D–E is another).

Those four half steps can also be written as a diminished fourth, as in C–F♭, but they sound the same, and you will almost always see a major third. This is the interval that gives the C major chord its major character.

How many half steps are in an octave

An octave spans 12 half steps, or 6 whole steps. It is the distance from a note to the next higher note with the same name, for example from one C to the next C.

Check it on the piano: start on a C key and move up one key at a time, without skipping any white or black keys. Each step is a half step. From one C, counting that key, to the key before the next C, there are 7 white keys and 5 black keys, 12 in total; the 13th key is the next C. That is why an octave spans 12 half steps even though its name means eight: it counts note names, not half steps.

The major scale divides that octave into five whole steps and two half steps (whole step, whole step, half step, whole step, whole step, whole step, half step), which also add up to 12 half steps.

The fifth interval: the perfect fifth

A perfect fifth is the interval of 7 half steps, or three and a half whole steps, between a note and the fifth note of its scale, as in C–G. It is the most stable interval after the octave.

Why the fifth matters

• Chords: it is the note that completes the triad, along with the root and the third. Rock power chords use only the root and fifth.
• Keys: the circle of fifths arranges keys by ascending fifths.
• Tuning: violin strings are tuned in fifths: G, D, A, and E. To tune it yourself, see how to tune a violin.

Compound intervals and inversions

Intervals larger than an octave are called compound: a ninth is an octave plus a second; a tenth is an octave plus a third. To find the simple equivalent, subtract 7 from the number.

To invert an interval, move the lower note up an octave. C–E, a major third, becomes E–C, a minor sixth. There are two rules:

• The numbers add up to 9: a second becomes a seventh, a third a sixth and a fourth a fifth.
• The quality reverses: major becomes minor, augmented becomes diminished, and perfect stays perfect.

This has a direct application: a major chord is built with a major third and a minor third above it (C–E–G); a minor chord reverses that order (C–E♭–G).

How to recognize intervals by ear using songs

The most common trick is to associate each interval with the beginning of a familiar melody. These are common ascending references:

For descending intervals, use Beethoven's “Para Elisa” (minor second), the Beatles' “Yesterday” (major second), “Hey Jude” (minor third), the opening of Beethoven's Fifth Symphony (major third) and Mozart's “Pequeña serenata nocturna” (perfect fourth). If one is unfamiliar, replace it with a song you know: a personal reference works better than someone else's. Once you know them well, test yourself with our free ear training tool.

Intervals are just one part of a musical ear; how to train your musical ear offers a 12-week plan that adds scale degrees, chords and dictation.

A 10-minute interval training routine

1. Start with a few very different intervals: major second, major third, perfect fifth and octave.
2. Play a note on a piano or an app, sing the interval while thinking of its reference song, then check by playing the second note.
3. Repeat from other starting notes. To check that you reached the right note, you can sing it into the tuner.
4. Ask someone, or an ear training app, to play random intervals, and record how many you identify correctly.
5. Once you recognize the first ones well, add minor thirds, fourths and sixths; then sevenths and the tritone.
6. Move on to harmonic intervals, with both notes sounding together, and descending intervals.
7. Apply it to your repertoire: find the intervals in the melodies you play or sing.

Interval recognition is part of solfège and is often tested alongside dictation in music degree entrance exams. If you are preparing, see our music entrance exam preparation course; to build this foundation from scratch, music theory lessons cover it step by step.

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