How this calculator works
Roman numerals describe chords by their position in a scale, so the same progression works in any key. Upper-case numerals are major chords, lower-case are minor, and a small circle marks a diminished chord. In a major key I, IV and V are major, ii, iii and vi are minor, and vii is diminished. A minor key uses the natural minor scale, so i, iv and v are minor and III, VI and VII are major. Pick a key and the numerals become real note names, which is how a progression written for one song gets transposed to suit a singer.
Formula
major key offsets from the tonic: I 0, ii 2, iii 4, IV 5, V 7, vi 9, vii° 11. minor key offsets: i 0, ii° 2, III 3, iv 5, v 7, VI 8, VII 10. Each chord takes the note at its offset plus the quality suffix: nothing for major, m for minor, dim for diminished.
Worked example
The 50s progression I-vi-IV-V in C major is C, Am, F, G. The same numerals in G major give G, Em, C, D. A ii-V-I turnaround in D major is Em, A, D. In A minor the Andalusian cadence i-VII-VI-v gives Am, G, F, Em; players often raise the last chord to E major for a stronger pull back to Am.
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Frequently asked questions
Why are some numerals upper case and some lower case?
The case shows the chord quality. Upper case is a major triad, lower case a minor triad, and a circle means diminished. The case is decided by the scale, not by the player, so a vi chord is minor because the sixth degree of the major scale forms a minor triad.
Can I use a progression in a different key?
Yes, that is the point of roman numerals. Choose another key and the same numerals produce the same relationship with different note names. A song in C can be moved to G by reading the same numerals from a G root, which suits a different vocal range.
Why does the minor mode use the natural minor scale?
Natural minor gives the plain pattern of that scale. Harmonic minor raises the seventh to make the dominant chord major, which is common in classical harmony, and the Andalusian cadence often uses that raised chord. Add or change numerals in custom mode to get those chords.
How do I save a progression I made?
The page keeps the values in the address bar, so the link reproduces the same key, mode and numerals. Share the link, or write the numerals down and enter them again on any device.