The 12 bar blues is one of the most enduring chord progressions in the history of popular music. It's the foundation of blues, rock and roll, jazz, and countless songs across every genre that traces roots to American music.
The Basic Structure
The progression is 12 bars long and uses three chords: the I, IV, and V of a key. In the key of A:
| Bar | Chord |
|---|---|
| 1 | A7 |
| 2 | A7 |
| 3 | A7 |
| 4 | A7 |
| 5 | D7 |
| 6 | D7 |
| 7 | A7 |
| 8 | A7 |
| 9 | E7 |
| 10 | D7 |
| 11 | A7 |
| 12 | E7 (turnaround) |
The I chord gets 4 bars, the IV chord gets 2, back to I for 2, then V–IV–I for bars 9–11. Bar 12 uses the V chord as a turnaround — it creates tension that pulls you back to the start of the progression.
Why Dominant 7th Chords?
All three chords are dominant 7th chords (A7, D7, E7) — not just plain major chords. Dominant 7ths have a slightly tense, unresolved quality that's central to the blues sound. Using them on I, IV, and V bends the strict rules of diatonic harmony, but that's the blues — it lives in the space between major and minor.
The Quick Change
A common variation moves to the IV chord in bar 2 instead of staying on I for 4 bars:
- Bars 1–2: I7 – IV7
- Bars 3–4: I7 – I7
- Bars 5–6: IV7 – IV7
- Bars 7–8: I7 – I7
- Bars 9–10: V7 – IV7
- Bars 11–12: I7 – V7
The "quick change" to IV in bar 2 adds movement and is very common in uptempo blues and rock and roll.
Common Keys for 12-Bar Blues
Blues is most commonly played in A, E, G, C, and B♭. A and E are the default for guitar (open string roots make them physically easy). B♭ is common in jazz and horn-based blues.
Beyond 12 Bars
Variations exist: 8-bar blues, 16-bar blues, and the jazz "bird blues" that adds ii–V substitutions throughout. But the 12-bar structure is the canonical form. Once it's internalized, you can sit in with virtually any blues or rock band with minimal communication — the form is shared cultural knowledge.
Using It in Your Songwriting
The 12-bar blues is a starting point, not a cage. You can write over it without it sounding dated by bringing your own rhythmic feel, melodic approach, and lyrical content. The form has been used for everything from Robert Johnson to Chuck Berry to B.B. King to early Beatles. The structure is predictable; the expression is all yours.