Chord Progression Calculator
From Roman Numerals to Real Chords
Songwriters and theory teachers describe progressions in roman numerals — "a I-V-vi-IV progression" — because the pattern works in any key. But to actually play it, someone has to translate those numerals into real chord names for a specific root note. This calculator does that translation, building the diatonic chords of a major or natural minor scale and mapping a numeral sequence onto them.
The Formula
Chord Quality per Degree = fixed diatonic pattern
Major: I, ii, iii, IV, V, vi, vii°
Minor: i, ii°, III, iv, v, VI, VII
The major scale is built from the semitone pattern 0, 2, 4, 5, 7, 9, 11 above the root; natural minor uses 0, 2, 3, 5, 7, 8, 10. Each scale degree then takes on a fixed quality — major, minor, or diminished — that never changes regardless of key, which is why the same roman-numeral progression sounds structurally identical in any key.
Where This Calculation Matters
- Transposing a progression to a singer's range — a I-V-vi-IV progression written for C major can be instantly re-derived in E♭ or G for a different vocalist.
- Songwriting — testing how a numeral pattern sounds in different keys, or building a progression from scratch using known-good numeral sequences.
- Learning functional harmony — seeing the same numerals resolve to different chord names in different keys reinforces how scale degree, not absolute pitch, defines harmonic function.
- Cover songs and transcription — identifying a song's progression in roman numerals makes it easy to play in whatever key suits the performer.
| Degree | C Major chord | A Natural Minor chord |
|---|---|---|
| I / i | C | Am |
| II / ii | Dm | Bdim |
| III / iii | Em | C |
| IV / iv | F | Dm |
| V / v | G | Em |
| VI / vi | Am | F |
| VII / vii | Bdim | G |
Derived directly from the scale-degree formula above; C major and A minor share the same key signature, so the two columns use the same underlying notes.
How to Use This Calculator
- Enter the root note of the key (such as C, F#, or Bb).
- Choose the scale — major or natural minor.
- Enter the progression as roman numerals separated by spaces, commas, or dashes (for example, "I V vi IV" or "i-VII-VI").
- Select Calculate to get the real chord names for that progression in the chosen key.
Related Calculations
Check the exact distance between any two chord tones with the Interval Calculator, or work out a song's total runtime once you know its tempo and bar count using the Song Length Calculator.