American Lutherie #111 featured an article I wrote about all of the properties of the geometry of the flattop guitar that combine to determine the total height of the bridge and saddle over the surface of the top of the instrument.^{1} That article included a number of diagrams and all the math needed to make bridge height calculations for most styles of flattop guitar. This page includes a calculator that will do all of those calculations for you - you just fill in the blanks and press the Calculate button. For the most part the descriptions of the parameters here are self explanatory, but for all practical purposes you'll need to reference the article for its diagrams and terminology before using this calculator.

Initial appearance: September 9, 2012

Last updated:
September 11, 2018

The formulae for calculating bridge height as a function of the construction geometry of a flattop guitar are:

${h}_{a}=2s\phantom{\rule{0ex}{0ex}}$

${h}_{b}={b}_{n}+f$

${h}_{t}=\frac{{b}_{n}-{b}_{e}}{{l}_{\mathrm{ne}}}*l$

${l}_{\mathrm{jb}}=\frac{l}{{2}^{n/12}}$

${h}_{n}=\mathrm{sin}\left(a\frac{\pi}{180}\right)*{l}_{\mathrm{jb}}$

$i={r}_{t}-\sqrt{{r}_{t}^{2}-{\left(\frac{{l}_{\mathrm{jt}}}{2}\right)}^{2}}$

$d=i+\sqrt{{r}_{t}^{2}-{\left({l}_{\mathrm{jb}}-\frac{{l}_{\mathrm{jt}}}{2}\right)}^{2}}-{r}_{t}$

${l}_{r}=\frac{l-\frac{l}{{2}^{n/12}}-0.056l}{2}$

${r}_{r}=\frac{{s}_{r}^{2}+{l}_{r}^{2}}{2{s}_{r}}$

${h}_{r}={r}_{r}-\sqrt{{r}_{r}^{2}-{\left(l-{l}_{\mathrm{jb}}\right)}^{2}}$

$h={h}_{a}+{h}_{b}-{h}_{t}+{h}_{n}-d+e-{h}_{r}$

where:

If values for l_{ne} and l_{jt} are specified, the calculator can check for collision between the top and the underside of the fretboard. Note that a collision or a lack thereof is not necessarily a good or bad thing, but must be accounted for in the construction of the instrument. Again, see the referenced article for more information about this.

Mottola, R.M. “Fretboard/Top Plate Geometry of the Flattop Guitar” American Lutherie, #111