The twelve bar Blues progression is the most common chord sequence used in Blues. There are many variations of this progression. This one consists of four bars of the 1 chord, two bars of the 4 chord, two bars of the 1 chord, one of the 5 chord, one bar of the 4 chord and two bars of the 1 chord.
To play the above progression in the key of A, substitute the symbols 1, 4 and 5 with the three basic chords in the key of A (A, D and E), as shown in the table.