Twelve bar blues is a typical blues chord progression, taking twelve 4/4 bars to the verse.
T T T T S S T T D S T TMany variations are possible. For instance, seventh chords are often used just before a change, and more changes can be added. A more complicated example might look like this, where "7" indicates a seventh chord:
T S T T7 S S7 T T7 D S T D7When the last bar contains the dominant, that bar can be called a turnaround.
Finally, here is an example showing the pattern in the key of D, and how it fits with the lyrics of a given verse. One chord symbol is used per beat, with "-" representing the continuation of the previous chord:
D - - - Woke up this morning with the
G - - - D - - - D7 - - - blues down in my soul
G - - - Woke up this morning with the
G7 - - - D - - - D7 - - - blues down in my soul Saying "My
A - - A7 baby gone and left me, got a
G - - G7 D - - - D - A A7 heart as black as coal"