The 12 bar blues form
One time through the form is twelve bars (measures), usually counted in four beats each. In Roman numerals, I is the chord named after the key, IV is the chord four letters up, and V is the chord five letters up:
| Bars | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Chord | I | I | I | I |
| Bars | 5 | 6 | 7 | 8 |
| Chord | IV | IV | I | I |
| Bars | 9 | 10 | 11 | 12 |
| Chord | V | IV | I | V |
Notice the shape: four bars at home, two away, two home, then a short trip (V, IV) back to home. Your ear learns the pattern quickly, which is why a band can start a blues with almost no rehearsal.
The chords in A, E, G and C
Blues chords are usually dominant 7th chords (A7, not plain A), which give the form its gritty, unresolved sound. Swap the Roman numerals for the chords of your key:
| Key | I | IV | V |
|---|---|---|---|
| A | A7 | D7 | E7 |
| E | E7 | A7 | B7 |
| G | G7 | C7 | D7 |
| C | C7 | F7 | G7 |
So a 12 bar blues in A is: A7 / A7 / A7 / A7 / D7 / D7 / A7 / A7 / E7 / D7 / A7 / E7. The same I-IV-V logic comes straight from the chords of a major key, the idea behind the circle of fifths.
Open 7th shapes for A and E
A and E are the favorite blues keys because every chord you need has an open shape. Columns run low E string to high E string; x means do not play that string.
| Chord | 6th | 5th | 4th | 3rd | 2nd | 1st |
|---|---|---|---|---|---|---|
| A7 | x | 0 | 2 | 0 | 2 | 0 |
| D7 | x | x | 0 | 2 | 1 | 2 |
| E7 | 0 | 2 | 0 | 1 | 0 | 0 |
| B7 | x | 2 | 1 | 2 | 0 | 2 |
G and C need a little more finger work (F7 is usually played as a barre), so start in A or E.
Add the quick change
The most common variation is the quick change: play the IV chord in bar 2 instead of the I. In A that is D7 for one bar, then straight back to A7 for bars 3 and 4. The rest of the form is identical, and it makes the opening four bars feel like they are going somewhere.
Play a scale over the chords
Once the chords are steady, solo over them with the minor pentatonic or blues scale in the same root. Over a blues in A, that is the A blues scale or the A minor pentatonic. One box position lets you stay in one place on the neck for all twelve bars. To find where any key lives, the guitar scale finder guide walks through it.
Practice it with Fretkit
Fretkit's Progressions tab lets you pick a key, style and mood and play the chords back, and its circle of fifths lists progressions such as I–IV–V and 12-bar blues with real chord names in your key. Use them to hear how the I, IV and V sit together before you play, and the interactive fretboard to see your scale on the neck. The essentials are free, with an optional Pro unlock.
See your key's chords and scale on one neck
Fretkit shows scales and chord shapes on an interactive fretboard, with a circle of fifths and a Progressions tab to hear chords in your key. Free to start, native for iPhone, iPad and Mac.
Get Fretkit on the App StoreFrequently asked questions
What are the chords in a 12 bar blues in A?
A7, D7 and E7: the I, IV and V of A. Four bars of A7, two of D7, two of A7, then E7, D7, and two last bars of A7, with the final bar often E7 as a turnaround.
What is the easiest key for 12 bar blues on guitar?
A and E. Every chord has an open 7th shape, so you can play the whole form without a barre.
What is a quick change?
Playing the IV chord in bar 2 instead of staying on the I. In A, that is D7 in bar 2 and back to A7 for bars 3 and 4.