Free online chord analysis tool

Roman numeral analysis is the standard way musicians describe the chords of a key. Instead of naming a chord by its letter, you name it by the scale degree it is built on, written as a roman numeral: the chord on the first note is I, on the fifth note is V, and so on. This one idea makes harmony portable — a progression written in numerals works in every key at once — and it reveals what each chord is doing rather than just what it is called. Below is how the numerals work, the chords a key produces, the functions those chords carry, and the progressions they build.

What roman numeral analysis is

Take any key and build a chord on each note of its scale, using only notes from that scale. You get seven chords, one per scale degree, and each is labeled with the roman numeral of its degree. In C major the chord on the first degree, C, is I; the chord on the fifth degree, G, is V. The great advantage is transposability: because the numerals describe positions in a scale rather than fixed letters, the same sequence of numerals produces the same progression in any key. Learn a progression as numerals once and you know it everywhere.

Why numerals instead of chord names

A chord name like G major tells you the notes; a numeral like V tells you the role. Those are different kinds of information. If a song uses a I–V–vi–IV progression, that description holds whether the song is in C, in G, or in E flat — only the actual chords change, not the pattern. Musicians think in numerals because it lets them hear and discuss what a progression does independently of its key, transpose a song instantly, and recognize that two songs in different keys share the same underlying moves.

Upper case, lower case, and the quality symbols

The numeral itself carries the chord’s quality through a small set of conventions. An upper-case numeral means a major chord: I, IV, V. A lower-case numeral means a minor chord: ii, iii, vi. A lower-case numeral with a small circle after it, like vii°, means a diminished chord. And an upper-case numeral with a plus sign, like III+, means an augmented chord. So the numeral does double duty: its number tells you the scale degree, and its case and symbol tell you whether the chord is major, minor, diminished, or augmented. Reading a line of numerals, you can see the whole shape of a progression at a glance.

The seven chords of a major key

Build a triad on each degree of the major scale and the qualities always come out in the same pattern: major, minor, minor, major, major, minor, diminished. Written as numerals that is I, ii, iii, IV, V, vi, vii°. Because the pattern is fixed, it holds in every major key — only the letters change. The table shows it in C major, the key that uses no sharps or flats, with each chord’s numeral, symbol, and notes.

The seven chords of a minor key

The natural minor scale produces its own fixed pattern of qualities: minor, diminished, major, minor, minor, major, major, or i, ii°, III, iv, v, VI, VII. Notice the tonic chord is now minor and the diminished chord has moved to the second degree. The table shows this in A minor, the relative minor of C major, which uses the same seven notes but treats A as home. That shared note set is why the two tables contain the same seven chords in a different order and with different roles.

A note on the minor key’s dominant

The chords above use the pure natural minor scale, which gives a minor v chord on the fifth degree. In practice, composers very often raise the seventh degree of the minor scale to create a stronger pull back to the tonic, which turns that v into a major V — in A minor, an E major chord with a G sharp. This raised seventh comes from the harmonic minor scale, and it is why so much minor-key music you hear ends on a bright, tense dominant resolving home rather than the softer natural-minor version. It is the single most common alteration in minor-key harmony.

Tonic, subdominant, dominant: the three functions

Behind the seven chords lie three broad jobs, called functions. The tonic function, centered on I, is home — the chord of rest and arrival. The dominant function, centered on V, is the strongest tension, leaning hard back toward the tonic. The subdominant function, centered on IV, moves away from home and often sets up the dominant. Nearly every progression is a journey among these three roles: leave the tonic, build tension through subdominant and dominant, and return. Hearing a progression in terms of home, away, and pull toward home is often more useful than tracking every individual chord.

Why the dominant pulls so strongly

The V chord contains the leading tone, the seventh degree of the scale, which sits just a half step below the tonic and leans toward it with real urgency. That is what gives the dominant its restless character. Add a seventh to the V chord — making it a dominant seventh — and the pull sharpens further, because the added note also wants to resolve down by a step. This is why a V or V7 chord so reliably signals that a return to the tonic is coming, and why it is the engine of cadences at the ends of phrases.

Common progressions in numerals

Once you read numerals, the progressions that run through popular music become easy to name. The I–V–vi–IV progression underpins a huge number of pop and rock songs; because it is written in numerals, the same four chords describe all of them regardless of key. The ii–V–I is the fundamental cadence of jazz, walking through subdominant, dominant, and home. And the twelve-bar blues cycles through I, IV, and V in a fixed twelve-bar pattern that anchors blues and early rock and roll. Writing each of these as numerals shows why songs in different keys can feel like close relatives: they share the same numeral pattern.

Seventh chords in numerals

Roman numerals extend naturally to richer chords. Add a seventh to a triad and you attach a small 7 to its numeral: the dominant seventh on the fifth degree becomes V7, the major seventh on the tonic becomes I with a seventh, and so on. The case rules still apply, so a minor seventh chord keeps its lowercase numeral and a major one stays upper case. Seventh chords fill out the sound and, in the case of V7, sharpen the pull toward the tonic. Ninth, eleventh, and thirteenth chords stack further still and are labeled the same way, with the extension number after the numeral. The principle never changes: the numeral names the degree and quality, and any number after it names what has been added on top.

Cadences: how phrases end

A cadence is the chord move that closes a musical phrase, and numerals name the common ones cleanly. A perfect cadence, V to I, is the strongest ending, landing firmly at home after the dominant’s tension. A plagal cadence, IV to I, is the softer “amen” ending heard at the close of hymns. A half cadence pauses on V, leaving the phrase hanging and expecting more. And an interrupted or deceptive cadence sets up V but resolves to vi instead of I, sidestepping the expected arrival for a gentle surprise. Because cadences are defined by numerals rather than specific chords, the same four patterns describe phrase endings in every key.

Secondary dominants, briefly

Progressions are not limited to the seven diatonic chords. One of the most common ways to step outside them is the secondary dominant — a chord borrowed to act as the V of a chord other than the tonic. Written as something like V/V (read “five of five”), it is the dominant that would resolve to the key’s own V chord, temporarily treating that chord as a momentary home. In C major, V/V is a D major chord that pulls toward G. Secondary dominants add color and momentary tension without leaving the key for long, and they are the first step most players take beyond plain diatonic harmony.

How the numerals connect to scales and chords

Roman numerals sit on top of the two ideas underneath them: scales and chords. The chords of a key come from stacking thirds on each note of its scale, which the scale finder lays out, and each individual chord’s construction is what the chord finder spells. Numeral analysis is the layer that names those chords by function so you can see how they move. If you want to build the same relationships by ear, the chord ear trainer drills recognizing chord qualities by sound, which is the skill that makes numeral analysis fast in practice.

Using it to analyze a song

To analyze a progression yourself, first find the key, then match each chord to its scale degree and write the numeral, using case and symbols for the quality. A song in C that moves C, G, A minor, F becomes I, V, vi, IV — and now you can transpose it to any key or compare it to other songs at a glance. This tool gives you the reference half of that process: pick the key and every diatonic chord appears with its numeral and notes, so you can match what you hear against the correct labels.

Using it with the other tools

Chord analysis ties the theory tools together. Click any numeral here to light the chord on the keyboard, or open the same chord in the chord finder to see how it is built from intervals. The scale finder shows the parent scale every one of these chords is drawn from, and the key signature finder confirms the key you are analyzing. To hear a progression in full, play the chords in order on the virtual piano, and to train your ear to recognize chords by sound, work through the chord ear trainer alongside this reference.