Type two notes to name the interval between them: quality, number, semitones, compound form, inversion and frequency ratio. Or pick a starting note and an interval to find the note above or below it, spelled correctly with sharps, flats or doubles.
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Find
Use # or b (x = double sharp, bb = double flat). Middle C = C4.
Choose a mode: interval between two notes, or note from an interval.
Type the notes like C4, F#3 or Bb (octave optional; middle C is C4).
For note-from-interval, pick the quality, the number (3 = third) and the direction.
Read the interval name, semitones, inversion and ratio.
Use the table to see every interval above or below the lower note.
Interval reference
Semitones
Interval
Short
Example from C
Inversion
Just ratio
0
Perfect unison
P1
C–C
Perfect octave
1/1
1
Minor second
m2
C–D♭
Major seventh
16/15
2
Major second
M2
C–D
Minor seventh
9/8
3
Minor third
m3
C–E♭
Major sixth
6/5
4
Major third
M3
C–E
Minor sixth
5/4
5
Perfect fourth
P4
C–F
Perfect fifth
4/3
6
Augmented fourth / diminished fifth
A4 / d5
C–F♯ / C–G♭
Diminished fifth / augmented fourth
45/32 / 64/45
7
Perfect fifth
P5
C–G
Perfect fourth
3/2
8
Minor sixth
m6
C–A♭
Major third
8/5
9
Major sixth
M6
C–A
Minor third
5/3
10
Minor seventh
m7
C–B♭
Major second
9/5 or 16/9
11
Major seventh
M7
C–B
Minor second
15/8
12
Perfect octave
P8
C–C′
Perfect unison
2/1
How interval names work
An interval name has two parts. The number counts letter names, both ends included: from D up to A is D-E-F-G-A, a fifth, whatever sharps or flats are attached. The quality compares the actual number of semitones with the reference interval of that number in a major scale built on the lower note:
Perfect (unison, 4th, 5th, octave): one semitone larger is augmented, one smaller is diminished.
Major (2nd, 3rd, 6th, 7th): one semitone smaller is minor, two smaller is diminished; one larger is augmented.
Example: E to C is a sixth (E-F-G-A-B-C). A major sixth above E is C♯ (9 semitones); E to C is 8 semitones, so it is a minor sixth.
Frequency ratio in equal temperament: ratio = 2^(semitones ÷ 12); the difference from just intonation in cents is 1200 × log₂(ET ratio ÷ just ratio).
Frequently asked questions
How do you find the interval between two notes?
Count the letter names from the lower note to the upper note, including both, to get the number (C to E is C-D-E, a third). Then count semitones and compare with the major or perfect interval of that number: C to E is 4 semitones, which is a major third; C to E♭ is 3 semitones, a minor third.
What is the difference between an augmented 4th and a diminished 5th?
Both span 6 semitones (a tritone) and sound the same on a piano, but they are spelled differently. C to F♯ is an augmented fourth (four letter names), while C to G♭ is a diminished fifth (five letter names). The spelling depends on the key and harmony.
Which intervals are perfect and which are major or minor?
Unisons, fourths, fifths and octaves (and their compound forms) are perfect, augmented or diminished. Seconds, thirds, sixths and sevenths are major, minor, augmented or diminished.
How do you invert an interval?
Move the lower note up an octave (or the upper note down). The numbers add up to 9 and the semitones to 12: a major third (4 semitones) inverts to a minor sixth (8 semitones). Major becomes minor, augmented becomes diminished and perfect stays perfect.
What is a compound interval?
An interval larger than an octave. Subtract 7 from the number for each octave to get the simple interval: a major tenth is a major third plus an octave, and a perfect twelfth is a perfect fifth plus an octave.
What frequency ratio does an interval have?
In equal temperament each semitone multiplies the frequency by the twelfth root of 2 (about 1.05946), so an interval of n semitones has the ratio 2^(n/12). Just intonation uses simple whole-number ratios instead, such as 3/2 for a perfect fifth and 5/4 for a major third.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.