What Is a Musical Interval? The Distance Between Notes

Interval names usually contain a number, such as second, third, fourth, fifth, or octave, along with a quality such as major, minor, perfect, augmented, or diminished. The number comes from counting letter names inclusively. From C to E, you count C, D, E, so the interval is some kind of third. The exact semitone distance tells you which quality it has.

For example, C to E is a major third, while C to E flat is a minor third. C to G is a perfect fifth. C up to the next C is a perfect octave. These names are the practical vocabulary behind a musical interval, and they let musicians discuss transposition, chords, scales, and melody with precision.

When two notes are played one after the other, the distance is a melodic interval. When they sound together, it is a harmonic interval. Your ear may experience the same interval differently depending on register, instrument, rhythm, and surrounding harmony. A perfect fifth in isolation can sound open and stable, but its effect changes when it appears inside a larger chord.

A musical interval also helps explain chord construction. A major triad contains a major third from the root to the third and a perfect fifth from the root to the fifth. A minor triad changes that lower relationship to a minor third. You do not need to calculate every chord this way forever, but interval thinking reveals why changing one note can change a chord's character.

Intervals can also be described by semitones, the smallest distance between neighbouring keys on a standard piano keyboard. A minor second spans one semitone, a major second spans two, and a perfect octave spans twelve. Semitone counting is especially useful for checking interval quality, but letter-name counting still matters for correct spelling. For example, two notes can sound the same on an equal-tempered instrument yet be written with different interval names because their musical function is different.

Interval recognition improves when you connect sound, notation, and singing:

• •Play two notes and name the interval before checking.
• •Sing a chosen interval upward from several starting pitches.
• •Practise descending intervals as well as ascending ones.
• •Notice intervals inside scales and chords you already know.
• •Compare similar sounds, such as major thirds and minor thirds.

Avoid relying only on famous-song shortcuts. They can help at first, but context can make the same interval feel different. When learning about a musical interval by ear, sing the starting note, imagine the second note, then check it on an instrument or app. Practising both upward and downward intervals makes the skill more flexible and useful in real music.

Every pitch is a vibration with a frequency, and intervals correspond to ratios between frequencies. An octave doubles the frequency, so the A above concert A at 440 hertz vibrates at 880 hertz. A perfect fifth is close to a ratio of 3 to 2, and a perfect fourth is close to 4 to 3. Ancient Greek thinkers linked to Pythagoras studied these simple ratios using strings of different lengths. Simple ratios tend to sound smooth because many of the overtones of the two notes line up, while more complex ratios produce clashing overtones that our ears hear as tension.

Modern keyboards use equal temperament, which splits the octave into twelve exactly equal semitones so you can play in every key. The cost is that most intervals are slightly out from the simple ratios. An equal-tempered fifth is extremely close to 3 to 2 and hard to tell apart, but an equal-tempered major third is noticeably wider than the pure ratio of 5 to 4. Singers, string players and barbershop quartets often adjust thirds by ear to make chords ring more cleanly, which is why the same chord can sound subtly different on a piano and in a choir.

If you move the lower note of an interval up an octave, you get its inversion, and the results follow a neat pattern. The two interval numbers always add up to nine, and the semitones always add up to twelve. C up to E is a major third of four semitones. Move the C up an octave and E up to C becomes a minor sixth of eight semitones. Major intervals invert to minor ones and the other way round, augmented intervals become diminished, and perfect intervals stay perfect, so a perfect fifth inverts to a perfect fourth.

Inversion is a handy shortcut. A major seventh can be hard to picture, but it is simply one semitone short of an octave, so you can find it by going up an octave and stepping down a semitone. One interval is its own mirror image. The tritone of six semitones, spelled either as an augmented fourth or a diminished fifth, inverts to the other spelling and still splits the octave exactly in half. Intervals wider than an octave are called compound intervals. A ninth is an octave plus a second, so the D in a C9 chord is the same letter as the second above C, just an octave higher.

The interval of six semitones, the tritone, has a dramatic reputation. It is often said that medieval church authorities banned it as the devil in music, diabolus in musica. There is no evidence of any such ban. Medieval theorists did steer melodies away from it, because it was awkward to sing accurately and did not fit neatly into the system of six-note patterns, called hexachords, used to teach singing. Singers often lowered a B to B flat to avoid it. The famous Latin nickname, however, is not recorded until much later, with the earliest known uses dating from around the start of the eighteenth century.

Far from being forbidden, the tritone sits at the heart of ordinary harmony. A dominant seventh chord such as G, B, D and F contains a tritone between B and F. When those two notes move inwards, B up to C and F down to E, the tension resolves onto a C major chord, the most common cadence in Western music. Composers also use the interval for colour. The song Maria from West Side Story opens with a rising tritone that immediately resolves up a semitone, and the heavy rock band Black Sabbath built the slow, ominous riff of their 1970 song Black Sabbath around it.

A musical interval is the measured pitch distance between two notes. Interval names help you describe melodies, build chords, understand scales, and train your ear. Start with a few common intervals, connect their written shape to their sound, and add new ones slowly instead of trying to memorise the whole system at once.