How do you calculate a the radius of a guitar?

Answer 1

Radius on a guitar usually refers to the slight curvature of the surface of some fretboards, the arc of which is part of an imaginary circle. The radius of that circle is 12 to 17 inches for most steel-string acoustic Guitars, smaller and hence more curved for some electrics. The only practical way to measure it is with a special gauge. If you had a diagram of it, you could calculate it with Pythagoreus' theorem. A straight line connecting the two sides of the fingerboard is the hypotenuse of a right triangle with two equal legs that are also radii.