The blues scale is esentially a minor pentatonic scale with an added flat fifth. The blues scale formula is 1, b3, 4, b5, 5, b7. The easiest way to remember this scale is to think of it as the minor pentatonic and simply learn where the added notes are within the normal five minor pentatonic positions. The diagrams show the flat fifth note in blue to make it easy to compare.
Click on the required key for scale notes and fret position diagrams in each key