How this calculator works
A chord is a set of notes measured in semitones above a root. A major triad stacks four semitones then three, a minor triad three then four, and a diminished triad three then three. Seventh chords add another third, and extended chords add ninths, elevenths and thirteenths that keep climbing. The page spells each note by letter name and fits the accidental, so a C minor third is Eb rather than D# and an F# major third is A# rather than Bb. The degree column shows how each note functions: 1 is the root, 3 the third, 5 the fifth, 7 the seventh, and 9, 11 and 13 are the compound forms of 2, 4 and 6.
Formula
the notes of a chord are the root plus each interval in semitones. major triad 0 4 7; minor triad 0 3 7; augmented 0 4 8; diminished 0 3 6; suspended second 0 2 7; suspended fourth 0 5 7; sixth 0 4 7 9; dominant seventh 0 4 7 10; major seventh 0 4 7 11; minor seventh 0 3 7 10; ninth 0 4 7 10 14; eleventh 0 4 7 10 14 17; thirteenth 0 4 7 10 14 17 21.
Worked example
C major is the root C plus 0, 4 and 7 semitones, giving C, E and G, the degrees 1, 3 and 5. C minor changes the third to 3 semitones, giving C, Eb and G. G dominant seventh is G plus 0, 4, 7 and 10, giving G, B, D and F. The same shapes move to any root: D minor is D F A because the minor triad is three semitones then four.
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Frequently asked questions
Why is the seventh of a dominant chord flat?
The dominant seventh uses ten semitones above the root, which is a minor seventh. A major seventh chord uses eleven. The difference of one semitone is what gives the dominant seventh its tension and pull back to the tonic.
What do 9, 11 and 13 mean?
They continue the stack of thirds past the seventh: 9 is fourteen semitones above the root, 11 is seventeen and 13 is twenty-one. Because a ninth is two semitones plus an octave, it is written with the same letter name as the second degree. Extended chords are often voiced with some tones left out.
Why are some notes spelled with flats or double flats?
Chord tones take successive letter names, so the seventh above C is some kind of B. In C diminished seventh the note is B double flat, not A, because it must be a seventh. The page follows that rule, which matters when reading the chord in a key.
Can I choose a different spelling?
Yes, the note spelling field picks sharps or flats for the root. Db major and C# major contain the same pitches but are written differently, and musicians choose the spelling that fits the key. The chord tones follow the chosen root spelling.