#6: Intonation – the Physics and the practical!

You’ll need:

  1. A guitar with an adjustable bridge (acoustics more often than not are fixed – some are “compensated” which means that the adjustments have already been approximated).
  2. An electronic tuner.
  3. The CORRECT sized screwdriver (please be careful – I’ve scratched too many guitars by trying to “make do” with the wrong type of screwdriver and slipping into the finish!)
  4. Some new strings.

The Physics of it:

Intonation means “adjusting to pitch of an instrument, such as a guitar.”  Fundamentally this means making adjustments so that the guitar plays in tune all the way up the neck.  It is by its nature an approximation (the accuracy of the 12 tone scale is a whole other debate!!), but it’s a way of adjusting the guitar so that it plays the best that it can.

Do you remember as a kid plucking a rubber band?      ……. All those cool noises that you could make…..

You could vary the pitch by;

Do this This happens Factor
Shorten the band Pitch goes up Distance
Lengthen the band Pitch goes down Distance
Pull the band tighter Pitch goes up Tension
Relax the band Pitch goes down Tension
Use a thicker band Pitch goes down Size
Use a thinner band Pitch goes up Size

On a guitar it’s not so different.


  • Tension is fixed when you tune the guitar to pitch.
  • Size is fixed when you put the strings on the guitar


  • The only thing that we can alter is the length of the string.
  • Effectively this is what the frets do for most of the string’s length.

If you halve the length of a string the pitch of the note will go up by one octave.


The 12 fret (octave) – MUST be ½ way between the nut and the bridge of the guitar.  The effect of the distance on the pitch of the note becomes greater as the distance decreases, and this is why we have adjustable bridges on guitars – basically the frets 1-12 are “fixed” but any changes in distance tension or size will have a much more pronounced effect above the 12th fret!  The adjustable bridge gives us a way of basically making the best of a bad job!

Intonation Procedure:

  1. Tune the guitar to pitch.  (I’m assuming you’re using some form of electronic tuner for this).  Remember ALWAYS tune UP to pitch, if you go too sharp wind it back and start again.
  2. Play the note at 12th fret.   It should be exactly one octave above the open string note.
  3. If the tuner shows it as flat (lower in pitch) it means the distance from the bridge saddle to the 12th fret is too great.
  4. Adjust the bridge saddle using the little screws on the bridge, so that the saddle moves TOWARDS the 12th fret, shortening the distance, and so raising the pitch.
  5. Retune and check.
  6. If the note at the 12th fret is now sharp (higher in pitch) – the distance from 12th fret to bridge saddle is too short.
  7. Use the little screw again to move the saddle AWAY from 12th fret, so lowering the pitch.
  8. Retune and check.
  9. Eventually you’ll get it so that the open string and octave are in tune.
  10. Move onto the next string and repeat.


  1. It is VITAL that all this is done with the guitar held in a playing position, not on a stand or neck rest.  The weight of the neck affects the pitch of the string too, and will affect your adjustments.
  2. Once you think you’re finished stretch out the strings by pulling them away from the fretboard by about 2 inches (5 cm) this will force the bridge saddles into position(they sometimes don’t move fully because they get stuck in the bridge).  Recheck the open and octave notes, readjust if necessary.

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