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Chord Numbering System

In country and bluegrass music, it is very common to refer to chords in a progression by their chord number. Just like the notes of a diatonic scale are numbered from one to seven, we also use numbers (Roman numerals) to indicate a chord’s position relative to the scale and key. For example, the chords that belong in the key of C major would be labeled from one to seven as shown below.

I ii iii IV V vi vii°
C Dm Em F G Am Bdim

Note: It is standard to use uppercase Roman numerals for major chords and lowercase for minor chords. The small degree ° symbol to the right of the numeral represents a diminished chord.

Chords in Each Major Key

There is a simple way to use the chord numbering system to figure out what chords belong in a key. First, learn the chord order, or in other words, the type of chord assigned to each Roman numeral. For example, all major keys will have the same chords ordered from I to vii° as shown below.

I ii iii IV V vi vii°
Maj Min Min Maj Maj Min Dim

Next, select a key and list the seven notes of that key’s major scale below each Roman numeral. To illustrate, let’s list the notes of the G major scale (G – A – B – C – D – E – F#) in the diagram.

I ii iii IV V vi vii°
G A B C D E F#
Maj Min Min Maj Maj Min Dim

It’s as easy as that! Now we know that the IV chord in the key of G is the C major chord, the vi chord in the key of G is the E minor chord, the ii chord is A minor, and so on.

Chords in Each Minor Key

The same idea can be applied to the chords of a minor key. The only difference is the order of the chords below each Roman number. The chords of a natural minor key will be written as follows:

i ii° III iv v VI VII
Min Dim Maj Min Min Maj Maj

Chord Progressions

When you play guitar with other musicians, the chord numbering system is an easy way to communicate chord progressions. One of the most common progressions used in country and bluegrass music is the I – IV – V – I chord progression in the key of G. Here are some other common major key chord progressions you might hear in country and bluegrass.

  • I – vi – IV – V
  • I – ii – V – I
  • I – IV – I – vi – V – IV – I