Formula for neck width in relation to bridge spacing

[Steve Ezzo]

A couple of years back, I vaguely remember a post for a formula for laying out a neck. I think it was, neck width at the 14th fret is equal to the highest to lowest string spacing at the bridge. I also seem to remember that this works irregardless of the string spacing at the nut. Am I remembering correctly? Any other rules-of-thumb for neck layout that you'd care to share? Thanks!!!

[Mark Swanson]

That rule is a good place to start, but it's the 12th fret and not the 14th. I always lay it out first using that as a starting point and then double check twice to make sure it looks right, and take into account the players' preference too.

[Chuck Tweedy]

Yes, the rule of thumb: "the width of the neck at 12th = string spacing at saddle"
is a good guideline, but it is not perfect every time. I got burned by using it too literally - the customer wanted more FB width. Awfully hard to add width to a neck after the fact.

[Bob Gramann]

As the others said, the rule is a guide but I never cut wood based on it. When I do a new spacing combination, I always draw the strings from nut to saddle then draw the appropriate fingerboard under it. When I'm sure it's right, then I cut wood. I do my fingerboard drawings on a good piece of poster board and save them so I never have to do it again for that combination.

[Steve Ezzo]

Mark, thanks for the correction, and thanks to everyone for the good advice!

[Louie Atienza]

It's all proportional. If you know the string spread at the nut and bridge, you can figure out the string spread at any point; you just then add the edge-to-string distance. You need to first figure out the convergence point of the two outer strings.

So if your string spread is 2-1/4" at the bridge (I'll call B), and 1-1/2" at the nut (I'll call N), and you have a 25-1/2" scale (S) with 1/8" between the edge and string on both sides, then the convergent point from the bridge I'll call C1 would be

C1 = B / (B-N) * S
C1 = 2.25" / (2.25"-1.5") * 25.5" = 76.5"

C2 would be the convergent length from the nut, and you subtract S from C1

C2 = C1 - S
C2 = 76.5" - 25.5" = 51"

To find an arbitrary width (W) along the fretboard relative to the nut it is a simple ratio. You have that length to C2. So if your fretboard end was at 18", then C2 would be 69"

Thus

76.5" / 2.25" = 69" / W (we then cross-multiply)
W = 2.25" * 69" / 76.5"
W = 2.03" (this is the string spread 18" from the nut)

You then just add 1/8" on each side and you have about 2.28"...

It looks more complicated than it is, I just tried to show each step so you can see how I derived the answer...

So if you just used the strign spread at the bridge you'd be at least 1/32" too narrow; I actually taper the width between teh edge and string so it's slightly more toward the heel...

[Simon Magennis]

That rule is a good place to start, but it's the 12th fret and not the 14th. I always lay it out first using that as a starting point and then double check twice to make sure it looks right, and take into account the players' preference too.

Additionally according to the version I heard, the width of the strings at the 12th is the width of the neck at the nut. Mainly I follow whatever the plan says but as an amateur the actual spacing is whatever it ends up being.

[Mark Swanson]

I don't see that one, Simon. A standard width for a neck at the nut is 1-3/4" wide and most guitars have a string spacing over 2" at the 12th fret. Are you talking about classical guitars?

[Robert Smallwood]

You can go here: http://www.buildyourguitar.com/resource ... fbcalc.pdf

and plug in some standard measurements or your own numbers and get the answer.

The theory is explained elsewhere and also here.

[John Kingma]

You can go here: http://www.buildyourguitar.com/resource ... fbcalc.pdf

and plug in some standard measurements or your own numbers and get the answer.

The theory is explained elsewhere and also here.

This is what I have been using since I built my first neck. It's a great little tool.

There is also a great fret spacing calculator on the same site.