The 12-bar blues is a fixed structure: twelve bars of 4/4, three chords, a standard chord order, and a specific place for the turn-around. In E major the chords are E7, A7, B7 (all dominant sevenths, which gives the blues its bite).

The form

Bar by bar in E blues:

1. Bars 1-4: E7 E7 E7 E7
2. Bars 5-6: A7 A7
3. Bars 7-8: E7 E7
4. Bar 9: B7
5. Bar 10: A7
6. Bars 11-12: E7 B7 (the turn-around)

In Roman-numeral shorthand: I7-I7-I7-I7 IV7-IV7-I7-I7 V7-IV7-I7-V7.

Why dominant sevenths throughout?

The blues predates common-practice functional harmony as a formal object; it comes from the field-holler and work-song tradition. The dominant-seventh chord on every degree is not wrong in tonal theory, it is a stylistic feature of the blues language. The flattened seventh in the melody, and the dominant-seventh quality in the harmony, are the two features that make blues sound like blues.

The blues in every key

• Key of C: C7, F7, G7
• Key of G: G7, C7, D7
• Key of D: D7, G7, A7
• Key of A: A7, D7, E7
• Key of E: E7, A7, B7 (the guitar key)
• Key of B♭: B♭7, E♭7, F7 (the sax key)
• Key of F: F7, B♭7, C7

Turn-around variations

Bars 11-12 are the turn-around. Three common patterns:

• Standard: I7 V7 (in E: E7 B7)
• Quick change: bar 2 becomes IV7 instead of I7. Adds early movement.
• Jazz turn-around: I7 VI7 ii7 V7 (in E: E7 C#7 F#m7 B7). Adds harmonic motion for a jazz-blues.

Play the blues in the tool

Open the chord progression generator, switch to the blues preset, pick a key. All twelve bars will play through in that key.