Free Online Musical Interval Calculator
Identify the interval between two notes and its semitones.
Frequencies assume equal temperament with A4 = 440 Hz. The interval is named from the lower note to the higher note, with the direction shown separately.
About the Musical Interval Calculator
An interval is the distance between two pitches. Musicians describe intervals by a number and a quality, such as a major third, a perfect fifth, or a minor seventh. The number counts letter names inclusively, while the quality distinguishes the exact size in semitones. This calculator converts two selected notes into an interval name, the number of semitones, the quality, the inversion, the size in cents, and the frequency ratio. It also plays the two notes together or one after the other so you can connect the visual result with the sound.
Counting semitones
In equal temperament, the smallest standard interval is the semitone, the distance between adjacent keys on a piano. Two semitones make a whole tone. A major third spans four semitones, a perfect fourth spans five, a perfect fifth spans seven, and a perfect octave spans twelve. Because the names are based on letter counting and the semitone count is based on pitch, the same semitone distance can receive different names depending on spelling: six semitones can be an augmented fourth or a diminished fifth. This tool uses the common equal-tempered labels and notes that the tritone is ambiguous by nature.
Quality and interval names
The quality of an interval depends on how it relates to the major or perfect scale. Seconds, thirds, sixths, and sevenths can be major or minor; when widened by a semitone they become augmented, and when narrowed they become diminished. Fourths, fifths, and octaves are perfect when they match the pure diatonic size; they become augmented when widened and diminished when narrowed. Unisons follow the same perfect rule. The calculator maps each semitone count from zero to twenty-four to its conventional name, including compound intervals such as the major ninth and perfect twelfth.
Inversion
Inverting an interval means moving the lower note up an octave or the higher note down an octave. The number of the inverted interval is the complement to nine in diatonic terms, or twelve minus the semitone count in chromatic terms. A perfect fifth (seven semitones) inverts to a perfect fourth (five semitones). A major third (four semitones) inverts to a minor sixth (eight semitones). Inversion preserves the total span of an octave, which is why the two intervals always add up to twelve semitones. Compound intervals invert within the octave after the extra octaves are removed.
Cents and frequency ratios
A cent is one hundredth of an equal-tempered semitone, so an equal-tempered fifth is exactly 700 cents and an octave is 1200 cents. The frequency ratio of an interval is 2(semitones / 12). A perfect fifth is therefore about 1.4983, slightly narrower than the pure 3:2 ratio of 1.5. The difference is about two cents, which is small but audible to trained listeners. These small discrepancies are the reason pianos are tuned with stretched octaves and why ensembles sometimes adjust intonation by ear.
Frequently asked questions
What is the difference between a major and minor interval?
A major interval is one semitone wider than the corresponding minor interval. For example, a major third is four semitones and a minor third is three. The quality describes that difference, not the size of the number.
Why is the tritone ambiguous?
Six semitones can be written as an augmented fourth or a diminished fifth depending on the letter names and the harmonic context. The sound is the same in equal temperament, but the spelling affects how the interval resolves.
Are compound intervals named differently?
Yes. A ninth is an octave plus a second, a tenth is an octave plus a third, and so on. The semitone count still determines the size, and the calculator reports whether the interval is simple or compound.