What is the 12-bar blues?
The 12-bar blues is a chord progression that repeats every 12 bars and forms the backbone of blues, rock and roll, and jazz. Nearly every famous blues song (Hound Dog, Johnny B. Goode, Sweet Home Chicago) runs on this same pattern.
The three chords you need are called the I, IV, and V chords. In the key of A, those are A, D, and E. In the key of E, they're E, A, and B. You can play this in any key, but A and E are the easiest starting points on guitar.
The key of A
For the key of A, you'll use A7, D7, and E7. The dominant 7th voicing gives blues its characteristic gritty feel. If you only know the plain open-chord versions of A, D, and E right now, those work perfectly fine to get started.
Start in the key of A
A and E are the friendliest keys for blues on guitar because the open strings reinforce the root notes naturally. Most beginner blues tutorials use A for this reason.
The 12-bar map
Write out 12 bars in a row. Each bar gets four beats. Here's the standard pattern using Roman numerals: I I I I / IV IV I I / V IV I V. That last bar is the turnaround: it loops you back to the top.
In the key of A that looks like this
Bars 1–4: A / Bars 5–6: D / Bars 7–8: A / Bar 9: E / Bar 10: D / Bar 11: A / Bar 12: E (turnaround back to bar 1).
Count evenly: one, two, three, four, one, two, three, four. Strum one downstroke per beat while you get the map in your head before worrying about rhythm or tone.
The quick change
Many blues tunes use a quick change: jumping to IV in bar 2 instead of staying on I. You'll hear both. The version above is the slow change and is simpler to learn first.
Adding a shuffle feel
Straight strumming sounds stiff. Blues lives in the shuffle rhythm, also called swing eighth notes. Instead of dividing each beat into two equal halves, you lean on the first and clip the second: long-short, long-short. It sounds like a train rolling.
The blues shuffle strum pattern
Say the word "trip-let" out loud and tap on beat one and three of that word: "TRIP let". That uneven lilt is the shuffle feel. Once you hear it you can't unhear it.
A classic beginner move is the low-string shuffle riff on the A string: fret the A string at the 2nd fret with your first finger, then rock your third finger between the 4th and 5th frets to alternate two notes in that long-short shuffle rhythm. This one riff across three strings IS the 12-bar blues for many players.
Slow it down first
Set a metronome to 60–70 BPM. The shuffle riff should feel completely relaxed in your hand before you speed up. Tension is the enemy of blues groove.
Play along and go further
The fastest way to make the 12-bar pattern stick is to play along with a backing track. Search for a slow blues backing track in A on YouTube and run through the progression while the track plays. You'll be surprised how musical even three simple chords sound over a groove.
Where to go next
Once the progression feels automatic, explore the minor pentatonic scale for soloing. It fits perfectly over the 12-bar blues in the same key. From there, learn the blues scale (pentatonic plus one extra note called the blue note) and you'll have everything you need to improvise.
Same pattern, infinite music
Stevie Ray Vaughan, B.B. King, Chuck Berry, and Eric Clapton all built careers on this one progression. The goal isn't to master the pattern and move on. Go deeper into what you can express within it.