Chord formulas refer to the actual notes being played in a chord and associates the numbers (1 through 8 ) of the major scale to those notes. Actually sometimes we repeat the scale an octave higher and continue counting up to number 13.
Major Chords. For example, the C major chord is comprised of the notes C, E and G. When we look at the C major scale, we notice that these are notes numbered 1, 3, and 5. We then can deduce that the ‘chord formula’ of the major chord is 1,3,5. If we want to know the notes of any major chord, we can jump to that chord’s major scale and find notes 1,3,5 and know which notes we are playing. Thus the G chord is played by notes G, B, D. The D chord is comprised of notes D, F#, A. Etc.
Minor Chords. A minor chord takes the the 3rd note of the major chord and “flats” it, or lowers it a half step. It’s chord formula is 1,♭3,5. We can look at the C scale, and take the notes C, E♭, and G. ‘E’ is the 3rd note which gets “flatted”, and becomes an ‘E♭’ to make the Cm chord. The Dm is comprised of notes D,F,A.
Other Chord Variations. Sometimes we see chords like C2, Csus, C6, C7, Cm7, Cmaj7, Cmaj9, Cadd9, etc. These notations refer to special ways of handling the numbered notes of the chord’s major scale. Look at the following chart:
|2 or sus2||1,2,5||C2 or Csus2||C,D,G|
|sus or sus4||1,4,5||Csus or Csus4||C,F,G|
See the next section, What Am I Playing on the Guitar?, to see how an example of how to incorporate chord formulas with chords you may already know.