Hi, thinking of building a guitar. I'm going to base my design loosely around the Ibanez S5521Q (Prestige). So firstly does anyone know the scale length of it/ sizes. And secondly, I read somewhere about an 18 rule, but i don't entirely understand it, so could some please explain how you calculate fret distance and what would be a suitable neck length to put 24 frets on it. The reason I was going to base my design of the Ibanez guitar was because it's roughly what I want.

Probably very badly worded, but any help would be appreciated


That Rule of 18 thing is basically where you take the scale length and divide it by 17.817154 to get the distance from the front of the nut to the center of the first fret. Then take that distance and subtract it from the total scale length and divide the answer by that same constant (17.817154) to get the distance from the center of the frist fret to the center of the second fret. Etc, etc...

This is a pretty crappy way to go about it because any miniscule error in measurement or calculation (rounding, for example) will compound itself as you move down the fretboard. As a result, most people use the Twelfth Root of Two formula because it is much more accurate and harder to fubar an entire fretboard. That formula is:


Where D is the distance from the front of the nut to the center of the next fret in question,
S is the scale length you are using,
and N is the fret number in question.
Units can be in inches, cm, mm, whatever as long as they all use the same unit.

As you can see, this formula references all measurements to the nut rather than to the previous fret.

This is about all I know, hope it helps.
Last edited by Invader Jim at Jun 22, 2014,
Very helpful, that pretty much answers all my questions. So yeah i'll stick with the scale length 25.5" and work it out from there. Thanks
Talk to StewMac -- there are templates for accurately placing frets AND the bridge. You want to have this information in hand before you begin building a guitar; otherwise you end up with a lovely guitar-shaped canoe paddle.