Why can the same number of semitones have two names?

Because intervals are measured in letter steps as well as in semitones. Three semitones from C to E flat is a third, since it spans three letters, while three semitones from C to D sharp is an augmented second, since it spans two. The sound is identical and the spelling is not.

What is the difference between a ratio and cents?

Both describe the same relationship. The ratio is the frequency of the upper note divided by the lower one, which is the form needed for arithmetic on frequencies. Cents are the logarithm of that ratio scaled so that an equal-tempered semitone is exactly a hundred, which makes intervals comparable at any pitch.

Why is a perfect fifth not exactly three to two?

Because equal temperament divides the octave into twelve identical steps, and no power of two to the one twelfth lands exactly on a simple ratio. The fifth comes out slightly narrow of three to two, by about two cents, which is the compromise that lets every key sound equally usable.

What happens if the two notes are more than an octave apart?

The interval is folded into a single octave, so the name stays within the twelve available. That is the form most useful for identifying a relationship, since a tenth and a third are the same interval with an octave added, but it does mean the octave count is not reported separately.

Can it tell me the interval of notes from a recording?

Not directly, because it works from typed note names. Measure the two frequencies first, then convert each to a note name with the note frequency calculator and enter those here, or work in cents if you want to skip the naming step.

Interval Calculator

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Interval Calculator names the distance between two notes and gives it three ways: in semitones, as a frequency ratio, and in cents. Enter any two notes and the relationship appears.

What is Interval Calculator?

Type a note in each field and the panel shows the interval name and its abbreviation, the number of semitones, the frequency ratio, and the distance in cents.

The result columns:

The interval name, drawn from the twelve names that cover an octave, from unison up to a major seventh.
The short form of that name, which is what appears on a chart.
The semitone count, which is the integer distance in the twelve-note scale.
The frequency ratio to four decimal places, and the same distance in centsas a whole number.

The three figures are the same relationship seen three ways. Semitones are the counting unit of the keyboard, so a perfect fifth is seven of them; the ratio is the frequency relationship, which for a perfect fifth in equal temperament is one point four nine eight three, close to but not exactly the three to two that a just fifth would be; and the cents figure is that same ratio on a logarithmic scale, where seven semitones come to exactly seven hundred. Cents are the most useful of the three when the question is how far apart two pitches actually sound, because a cent is the same proportional distance at every pitch, whereas a fixed number of hertz is a large interval low down and a tiny one high up. The ratio is most useful when the interval is going into arithmetic, such as working out where a filter or an oscillator should sit. One piece of musical spelling is visible in the result and worth knowing about. Intervals are counted from letter to letter, so the same number of semitones can carry different names depending on how the notes are written: C up to D sharp and C up to E flat are both three semitones apart, but one is an augmented second and the other a minor third. The tool reports what the two note names imply rather than only the distance, which is why the name and the semitone count can disagree with a naive reading of the interval.

Where it stops:

Octave equivalents are folded, so notes more than an octave apart read as the interval within one.
No inversion or compound naming beyond the folded form.
Equal temperament only, so a just or historically tempered interval differs from the ratio shown.
No audio input; the notes have to be typed.
Spelling depends on how you write the notes, not on how they sound.
Nothing is uploaded, and no history is kept.

Use it when a chart has to be understood rather than played: working out what a part is doing, checking whether two lines move by a third or a fourth, or finding the ratio to use for a harmonic relationship in synthesis. When a single pitch rather than a relationship is the question, the note frequency calculator covers that, and when the interval has to be measured in tuning terms rather than named, the cents calculator does the arithmetic directly. Both figures are exact, so the interval can be trusted as a reference for tuning or for working out a harmonic relationship between two pitches.

How to use Interval Calculator

Type the lower or first note in the first field, such as C4.
Type the second note in the second field, such as G4.
Read the interval name and its short form.
Use the semitone, ratio and cents columns for whichever form you need.

When to use Interval Calculator vs related tools

Interval Calculator is the tool for naming and quantifying the distance between two pitches, which is what a chart or a harmonic plan needs. Note Frequency Calculator converts a single note to a frequency instead. When the interval matters as a tuning offset rather than as a name, Cents Calculator works in that unit, and Chord Calculator stacks intervals into complete chords with their spellings.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.