Knowing the chords in a key is like having the answer key to most songs. If a song is in G, you already know the six or seven chords it will probably use before you hear it. This lesson is part of our music theory for guitar beginners series.
Short answer: to find the chords in a key, build a three-note chord (root, 3rd, 5th) on each of the seven notes of the major scale. The result always follows the same pattern: major, minor, minor, major, major, minor, diminished – written I ii iii IV V vi vii°. In G that gives G, Am, Bm, C, D, Em and F#dim.
🎸 Free download
Not sure which guitar is right for you?
Get the free Guitar Gear Cheat Sheet: match your style, budget and hands to the right guitar in 2 minutes. You’ll also get my 30-Day Practice Plan as a bonus.
Send My Cheat Sheet →Diatonic Chords Guitar Players Use Every Day
“Diatonic” means “belonging to the scale.” Diatonic chords on guitar are the chords you build using only the notes of one scale. Here is how it works in C major (C D E F G A B):
- Start on C and stack every other note: C–E–G = C major.
- Start on D: D–F–A = D minor (D to F is a minor 3rd).
- Start on E: E–G–B = E minor.
- Start on F: F–A–C = F major.
- Start on G: G–B–D = G major.
- Start on A: A–C–E = A minor.
- Start on B: B–D–F = B diminished (minor 3rd plus a flattened 5th).
The quality (major, minor or diminished) of each chord comes from the intervals inside it. A major chord has a major 3rd (4 half steps) on the bottom; a minor chord has a minor 3rd (3 half steps). If you want the deeper “why,” read how guitar chords work.
The Roman numeral system
Musicians number the chords with Roman numerals: uppercase for major, lowercase for minor, and a small circle for diminished. Because the pattern never changes, a I-IV-V in C (C-F-G) is the same progression as a I-IV-V in E (E-A-B). That is what makes transposing so simple.
Chords in the Key of G
G is one of the most guitar-friendly keys, so let’s look at the chords in the key of G in detail. The G major scale is G A B C D E F#.
| Degree | Numeral | Chord | Notes | Easy guitar shape |
|---|---|---|---|---|
| 1 | I | G major | G B D | Open G |
| 2 | ii | A minor | A C E | Open Am |
| 3 | iii | B minor | B D F# | Barre at 2nd fret (A-string root) |
| 4 | IV | C major | C E G | Open C |
| 5 | V | D major | D F# A | Open D |
| 6 | vi | E minor | E G B | Open Em |
| 7 | vii° | F# diminished | F# A C | Rarely used; D/F# is a common substitute |
Five of those chords are open shapes, which is why so many campfire, country and worship songs are in G. Popular progressions in G:
- G – C – D (I-IV-V)
- G – D – Em – C (I-V-vi-IV)
- Em – C – G – D (vi-IV-I-V)
- G – Em – C – D (I-vi-IV-V)
Chords in Every Common Guitar Key
Use this chart to find the chords in a key quickly. Keys are listed in the order guitarists use most.
| Key | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| C | C | Dm | Em | F | G | Am | Bdim |
| G | G | Am | Bm | C | D | Em | F#dim |
| D | D | Em | F#m | G | A | Bm | C#dim |
| A | A | Bm | C#m | D | E | F#m | G#dim |
| E | E | F#m | G#m | A | B | C#m | D#dim |
| F | F | Gm | Am | Bb | C | Dm | Edim |
Notice how the keys in this chart sit next to each other on the circle of fifths. Neighboring keys share most of their chords, which is why moving from G to D in a song sounds natural.