12 bar blues I //// //// //// I7 //// IV //// //// I //// //// V7//// I //// I // IV // I // V7 // The last two bars are called the turnaround

8 bar blues:

I //// V7 //// I //// IV //// I //// V7 //// I // IV // I // V7 //

16 bar blues I //// //// //// I7 //// IV //// //// I //// //// IV //// //// I //// //// I //// V7 //// I // IV // I// V7//

The first example is most commonly used.

The second example would be Trouble In Mind, Crow Jane, Keys To The Highway

The third example would be C.C. Rider

It must be said that often the bars are not rigidly adhered to. For some verses a traditional blues player might use an 11 i/2 bar blues or and 8 1/2 bar blues. Traditional blues players seem to know when the chords change intuitively.

Frank Hamilton