Free online interval finder

An interval is the distance between two notes, and it is the unit that scales, chords, and melodies are all measured in. Every chord is a particular set of intervals, every scale is a particular sequence of them, and playing by ear is largely a matter of recognising them, so intervals are worth understanding in their own right. Below is how intervals are measured and named, why some sound smooth and others tense, and how to start recognising them by ear.

What an interval is

Play two notes, either one after the other or together, and the gap between them is an interval. The simplest way to measure that gap is in half steps — the distance from one key to the very next, black or white. C up to the G above it, for instance, is seven half steps. Counting half steps tells you the exact size of any interval, and it is the measurement the finder uses under the more familiar names.

Size and quality

An interval’s full name has two parts. The number — second, third, fourth, and so on up to an octave — counts the letter names it spans, so C to E is some kind of third because it covers C, D, E. The quality — major, minor, perfect, augmented, or diminished — fine-tunes that by a half step. Seconds, thirds, sixths, and sevenths come in major and minor forms a half step apart: a major third is four half steps, a minor third three. Together the number and quality name every interval precisely, such as “major sixth” or “minor seventh”.

Perfect intervals

The unison, fourth, fifth, and octave are called perfect rather than major or minor, because they sound especially stable and are the same whether you are in a major or minor key. The perfect fifth — seven half steps, like C up to G — is the most consonant interval after the octave, which is why it anchors so many chords and why tuning is often checked against it. The perfect fourth is its mirror image, and the octave is the strongest consonance of all, the two notes blending almost into one.

Consonance and dissonance

Some intervals sound smooth and at rest — the octave, fifth, and thirds — while others sound tense and unfinished, like the minor second or the tritone (the interval that splits the octave exactly in half). That tension is not a flaw; it is what gives music movement, because a dissonant interval creates the expectation of resolving to a consonant one. Playing intervals here and listening for that pull is the fastest way to feel the difference rather than just label it.

The full set of intervals

Within one octave there are twelve intervals, one for each half step. Counting up from a root: one half step is a minor second, two a major second, three a minor third, four a major third, five a perfect fourth, six the tritone, seven a perfect fifth, eight a minor sixth, nine a major sixth, ten a minor seventh, eleven a major seventh, and twelve the octave. The seconds and thirds sound close and stepwise, the fourths and fifths open and stable, the sixths and sevenths wider and more expressive. Playing up this ladder here, one interval at a time, is the clearest way to hear how the distance grows.

The tritone

The interval of six half steps — the tritone — deserves a mention of its own because it splits the octave exactly in half and is the most tense interval in common use. Historically it was nicknamed the “devil in music” for how unstable it sounds, yet it is essential: it sits inside every dominant seventh chord, and its strong urge to resolve is a large part of what drives music from tension back to rest. Play it here and the pull to move is unmistakable.

Compound intervals

Intervals larger than an octave are called compound intervals. A ninth is an octave plus a second, an eleventh an octave plus a fourth, and so on. They matter most in harmony, where the extended chords stack notes into this range, but by ear a ninth behaves much like the second inside it, an octave higher. Recognising that a compound interval is “an octave plus something smaller” keeps even the wide ones easy to name.

Why some intervals sound smooth

Consonance is not a matter of taste alone; it has a physical basis. When two notes vibrate at frequencies related by a simple ratio, their waves line up often and the pair sounds smooth. The octave is a 2:1 ratio, the perfect fifth close to 3:2, the perfect fourth 4:3 — the simplest ratios, and the most consonant intervals. The more complex the ratio, the more the waves clash, which is why a minor second or a tritone sounds rough. That is the same reason the perfect fifth is used as a tuning reference: its simple ratio makes any error easy to hear.

How intervals build chords and scales

Intervals are the material everything else is made from. Stack two thirds and you have a triad, which is why the chord finder describes chords as patterns of thirds. Line up a specific run of whole and half steps — themselves just major and minor seconds — and you have a scale, which is what the scale finder lays out. Recognising the interval between two notes therefore tells you a great deal about the harmony around them, and any interval you find here can be played in full on the virtual piano.

Inverting an interval

Move the lower note of an interval up an octave, or the upper note down, and you invert it. A perfect fifth inverts to a perfect fourth, a major third to a minor sixth; the two always add up to an octave, and major swaps with minor while perfect stays perfect. This is more than a curiosity — it explains why a chord in different inversions still sounds like the same chord, and why some interval pairs feel closely related.

Harmonic and melodic intervals

The same interval can be played two ways. Sound both notes at once and it is a harmonic interval — you hear the two blending or clashing as a single colour, the basis of chords. Sound them one after the other and it is a melodic interval — you hear the leap between them, the basis of melody. The distance is identical either way; only the presentation changes. Pressing Play here sounds the two notes in turn, so you hear the melodic version, while holding both on the virtual piano lets you hear the harmonic one.

Diminished and augmented intervals

Beyond major, minor, and perfect, an interval can be stretched or squeezed by a half step to become augmented (a half step wider) or diminished (a half step narrower). These usually appear because of how a note is spelled rather than how it sounds: an augmented fourth and a diminished fifth are the same six-half-step distance — the tritone — written two different ways depending on the key. It is the interval equivalent of the enharmonic spelling that lets one key be called both C sharp and D flat.

Recognising intervals by ear

The classic trick is to anchor each interval to the opening of a song you already know: a perfect fourth opens “Here Comes the Bride”, a perfect fifth opens “Twinkle, Twinkle”, and an octave opens “Somewhere Over the Rainbow”. Play an interval here, hum the matching tune, and the sound starts to stick. When you want to test yourself without seeing the notes, the interval ear trainer plays an interval and asks you to name it, and the note finder helps if you need to place either note first.

Reading it on the keyboard

Pick a root note and an interval and both notes light up across the central octave, named, with the interval spelled out beneath. Press Play to hear the two notes one after the other. Use the flats toggle to read the upper note the way its key is normally written, since the same key can be spelled as a sharp or a flat.

Ways to practise with it

• Play an interval, then try to sing the top note from the bottom one before checking against the sound.
• Compare a major and a minor version of the same interval back to back to fix the half-step difference in your ear.
• Learn a song anchor for each interval, then move to the interval ear trainer to test recognition without the notes in front of you.