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Interval Calculator Music

Video & AudioMusic and Audio Theory

Letter A–G, then ♯/# or ♭/b (x or bb for doubles), then an octave number. No octave means octave 4.

Middle C is C4. A lower second note gives a descending interval.

Interval —
Short name
—
Semitones
—
Direction
—
Inversion
—
Equal-tempered frequency ratio
—
Cents
—

Type two notes with octave numbers and the calculator names the interval between them. C4 to G4 spans five letter names and 7 semitones, so it is a perfect fifth (P5); flip it and you get a perfect fourth. Spelling matters: C to F♯ is an augmented fourth, while C to G♭ is a diminished fifth, though both are 6 semitones.

About this tool

Theory students checking homework, arrangers voicing chords and guitarists working out a riff all need the same answer: what is the distance between these two notes, called properly? This calculator reads two spelled notes such as B♭3 and D5, counts the letter names to get the interval number, counts semitones to get the quality, and reports the full name with its short form (m3, A4, P8), the direction, the inversion, the size in cents and the frequency ratio in twelve-tone equal temperament. Compound intervals up to a double octave get their own names, such as major tenth. One limit: the ratio and cents assume equal temperament, so they differ slightly from just intonation, where a perfect fifth is exactly 3:2 rather than 1.4983.

How to use it

  1. Enter the first note

    Type a letter A–G, an accidental (# or ♯, b or ♭, x or bb for doubles) and an octave number, such as F#3. Middle C is C4.

  2. Enter the second note

    Type the note you are measuring to. If it is lower than the first, the interval is reported as descending.

  3. Read the interval and its working

    The name, short form, semitone count, inversion, cents and ratio update as you type, with the letter and semitone counts shown underneath.

Examples

C4 up to G4

First note
C4
Second note
G4

Result Interval: Perfect fifth
Short name: P5
Semitones: 7
Direction: Ascending
Inversion: Perfect fourth
Equal-tempered frequency ratio: 1.4983
Cents: 700

  1. Letter steps: C4 to G4 spans 4 letter steps, so the interval number is 4 + 1 = 5 (fifth).
  2. Semitones: MIDI 67 − 60 = 7 semitones.
  3. A plain fifth has 7 semitones; 7 is the same, so the quality is perfect.
  4. Equal-tempered ratio = 2^(7/12) = 1.4983 (700 cents).

Five letter names and seven semitones make the perfect fifth heard at the start of 'Twinkle, Twinkle'.

C4 to F♯4, the tritone

First note
C4
Second note
F#4

Result Interval: Augmented fourth
Short name: A4
Semitones: 6
Direction: Ascending
Inversion: Diminished fifth
Equal-tempered frequency ratio: 1.4142
Cents: 600

  1. Letter steps: C4 to F♯4 spans 3 letter steps, so the interval number is 3 + 1 = 4 (fourth).
  2. Semitones: MIDI 66 − 60 = 6 semitones.
  3. A plain fourth has 5 semitones; 6 is 1 more, so the quality is augmented.
  4. Equal-tempered ratio = 2^(6/12) = 1.4142 (600 cents).

Six semitones spelled C–F♯ is an augmented fourth; spell it C–G♭ and the same sound becomes a diminished fifth.

C3 to E4, a compound interval

First note
C3
Second note
E4

Result Interval: Major tenth
Short name: M10
Semitones: 16
Direction: Ascending
Inversion: Minor sixth (of the simple interval)
Equal-tempered frequency ratio: 2.5198
Cents: 1,600

  1. Letter steps: C3 to E4 spans 9 letter steps, so the interval number is 9 + 1 = 10 (tenth).
  2. Semitones: MIDI 64 − 48 = 16 semitones.
  3. A plain third plus 1 octave(s) has 16 semitones; 16 is the same, so the quality is major.
  4. Equal-tempered ratio = 2^(16/12) = 2.5198 (1600 cents).

An octave plus a major third gives a major tenth of 16 semitones, a common left-hand piano spread.

How it is calculated

number = letter steps + 1; semitones = MIDI(high) − MIDI(low); quality = semitones − reference size of a major or perfect interval of that number

letter steps
How many letter names the notes are apart, counting octaves as 7 each
MIDI
Note number: 12 × (octave + 1) + pitch class + accidentals
reference size
0, 2, 4, 5, 7, 9, 11 semitones for unison to seventh, plus 12 per octave
ratio
2^(semitones ÷ 12) in equal temperament; cents = semitones × 100

The number comes from letters only, so accidentals never change it. Unisons, fourths, fifths and octaves are perfect at their reference size and become augmented one semitone larger or diminished one smaller. Seconds, thirds, sixths and sevenths are major at the reference size, minor one smaller, diminished two smaller and augmented one larger. Inversion swaps major with minor and augmented with diminished, and the numbers add up to nine.

When not to use it

  • Microtonal or just-intonation work needs exact ratios, not the equal-tempered values shown here.
  • Naming a whole chord needs a chord identifier; this measures one pair of notes at a time.

Common mistakes

  • Counting semitones alone: C–E♭ and C–D♯ are both 3 semitones but are a minor third and an augmented second.
  • Forgetting that octave numbers change at C, so B3 is directly below C4, not B4.
  • Starting the count at zero: the first note itself counts as one, so C to E is a third.

Frequently asked questions

Why do C to F♯ and C to G♭ get different names?

They sound the same on a piano, 6 semitones, but the letter count differs. C to F covers four letter names, so it is a fourth; C to G covers five, so it is a fifth. The extra or missing semitone then makes them augmented and diminished respectively. In written music the spelling tells the reader which way the note resolves.

How are octave numbers assigned?

This tool uses scientific pitch notation, where middle C is C4 and the number increases at each C. So the B just below middle C is B3, and A4 is the 440 Hz tuning A. If you leave the octave off, the note is treated as octave 4.

What is a compound interval?

Any interval wider than an octave, such as a ninth (an octave plus a second) or a tenth (an octave plus a third). It keeps the quality of its simple version, so C3 to E4 is a major tenth because C to E is a major third. The inversion shown is that of the simple interval.

What does inversion mean here?

Inverting moves the lower note up an octave or the upper note down, so the two notes trade places. A major third becomes a minor sixth, a perfect fifth becomes a perfect fourth, and the two numbers always add up to nine.

Why is the fifth's ratio 1.4983 and not 1.5?

Modern keyboards use twelve-tone equal temperament, where each semitone multiplies frequency by the twelfth root of two. Seven of them give 1.4983, about 2 cents narrower than the pure 3:2 fifth of just intonation. Singers and string players often drift toward the pure ratio.

Can I type flats and sharps without special symbols?

Yes. Use # for sharp and a lowercase b for flat, x or ## for a double sharp and bb for a double flat. The symbols ♯, ♭, 𝄪 and 𝄫 work too. The note letter can be upper or lower case.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 12). Interval Calculator Music. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/video-audio/music-and-audio-theory/interval-calculator-music/

MLA

Tools Directory Editorial Team. “Interval Calculator Music.” Tools Directory, 12 Oct. 2026, https://tools.milunir.com/video-audio/music-and-audio-theory/interval-calculator-music/. Accessed 27 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Interval Calculator Music.” Tools Directory. Last modified October 12, 2026. Accessed October 27, 2026. https://tools.milunir.com/video-audio/music-and-audio-theory/interval-calculator-music/.

Link<a href="https://tools.milunir.com/video-audio/music-and-audio-theory/interval-calculator-music/">Interval Calculator Music – Tools Directory</a>