A music interval is the distance in pitch between two notes, measured in semitones and named by counting letter names. The interval from C to E is a major 3rd, four semitones, while C to G is a perfect 5th, seven semitones, and every chord and scale is built from intervals.
What is a music interval?
An interval is the distance between two notes, and it is the basic measuring unit of all music theory. Just as a builder measures in centimetres, a musician measures in intervals: the gap from C to E is a major 3rd, the gap from C to G is a perfect 5th, and the gap from C to the next C is an octave. Intervals have two properties, a size measured in semitones and a quality, major, minor, perfect, diminished or augmented, that describes the exact character of the distance. Intervals matter because everything else in music is made from them. A chord is a stack of intervals above a root, a scale is a sequence of intervals, and a melody is a journey from one interval to the next. If you understand intervals, you can build any chord from any root, work out any scale, transpose any song, and hear what is happening in music you listen to. Without intervals, music theory is a list of facts to memorise; with intervals, it is a system you can work out for yourself.
How intervals are measured
Every interval is measured in two ways at once. First, count the letter names from the lower note to the upper note, including both ends: C to E is C, D, E, three letters, so it is some kind of 3rd. Then count the semitones: C to E is four semitones, and a 3rd of four semitones is a major 3rd. C to Eb is also three letters, so it is also a 3rd, but it spans three semitones, so it is a minor 3rd. The letter count gives the number, and the semitone count gives the quality, and you need both to name an interval correctly. The qualities follow a pattern. Seconds, 3rds, 6ths and 7ths can be major or minor: the larger version is major and the smaller version is minor. Unisons, 4ths, 5ths and octaves are perfect, because they sound so stable that the major-minor distinction does not apply. If a perfect interval is narrowed by a semitone it becomes diminished, and if it is widened by a semitone it becomes augmented. The interval calculator measures any interval for you, the C major scale shows the intervals of a scale from its root, and the key of C major shows the chords those intervals build.
Worked example — intervals above G. Count letter names and semitones together. G to B is G, A, B, three letters, and four semitones, so it is a major 3rd. G to C is G, A, B, C, four letters, and five semitones, so it is a perfect 4th. G to D is five letters and seven semitones, a perfect 5th. G to F is seven letters and ten semitones, a minor 7th, while G to F# is seven letters and eleven semitones, a major 7th. Notice that the letter count never changes for a given number: a 7th above G is always some kind of F, and the semitones decide whether it is major or minor. The G major guitar chord is built from the major 3rd and perfect 5th above G.
How to practise intervals
Interval practice is mostly counting: letter names for the number, semitones for the quality. Drill it away from your instrument first, then check yourself on it.
- Pick a root note and name the major 3rd above it, then the perfect 5th, then the major 7th, counting semitones each time before you answer.
- Play two notes on your instrument and name the interval between them, starting with 3rds and 5ths, which are the easiest to hear, and check the 3rds against the G major scale.
- Write out the intervals above C, from the minor 2nd to the octave, and check them against the reference table below.
- Sing the interval before you play it: hum the root, then hum the note a perfect 5th above it, and check yourself against the piano.
- Use the interval calculator to test yourself on random intervals until you can name the number and the quality without counting on your fingers.
Common mistakes
- Counting semitones but not letter names — C to F# and C to Gb span the same six semitones, but one is an augmented 4th and the other is a diminished 5th. The letter count decides the number, so always count letters first.
- Calling every 3rd major — A 3rd can be major (four semitones) or minor (three semitones), and the difference matters: it decides whether a chord is major or minor. Count the semitones before you name the quality.
- Measuring intervals downwards the wrong way — An interval measured downwards is the inversion of the interval measured upwards: a major 3rd up is a minor 6th down. If you measure downwards, count the letters downwards too, or the number will be wrong.
Quick reference
This table lists every interval within one octave, measured from C, with the semitone count that decides its quality. Learn it as a ladder: each step up adds one semitone, and the quality changes at the steps where the number changes from major to minor or from perfect to diminished.
| Interval | Notes from C | Semitones |
|---|---|---|
| Minor 2nd | C – C# | 1 |
| Major 2nd | C – D | 2 |
| Minor 3rd | C – D# | 3 |
| Major 3rd | C – E | 4 |
| Perfect 4th | C – F | 5 |
| Tritone | C – F# | 6 |
| Perfect 5th | C – G | 7 |
| Minor 6th | C – G# | 8 |
| Major 6th | C – A | 9 |
| Minor 7th | C – A# | 10 |
| Major 7th | C – B | 11 |
| Octave | C – C | 12 |
Memorise the table by playing it on piano, starting from C and walking up the white and black keys one semitone at a time, naming each interval as you land on it. When you can name all twelve without looking, try the same ladder from G, and then from F#, where the spellings get harder but the semitone counts stay exactly the same.
Frequently asked questions
What is an interval in music?
An interval is the distance in pitch between two notes, named by counting letter names for the number and semitones for the quality. C to E is a major 3rd, four semitones, and C to G is a perfect 5th, seven semitones.
How many intervals are there?
Within one octave there are twelve interval sizes, from the minor 2nd (one semitone) to the octave (twelve semitones), and each size has a name. Beyond the octave, compound intervals continue the pattern: a 9th is a 2nd plus an octave, and so on.
What is the difference between a major and a minor interval?
One semitone. A major interval is one semitone wider than the minor version of the same number: a major 3rd is four semitones and a minor 3rd is three. Only 2nds, 3rds, 6ths and 7ths have major and minor forms.
What is a perfect interval?
A perfect interval is a unison, 4th, 5th or octave, which sounds exceptionally stable and consonant. These intervals are called perfect rather than major or minor, and if they are narrowed or widened by a semitone they become diminished or augmented.
Why do I need to learn intervals?
Because intervals are the building blocks of chords, scales and melodies. Once you can measure intervals, you can build any chord from any root, work out any scale, and transpose music, instead of memorising hundreds of separate facts.