When holding the guitar in your hand, you'll notice that the guitar neck is the rounded shape at the back, making it more comfortable to place your palm. Do you know that the front of the guitar neck, the guitar fretboard side, is also convex? The fretboard side is flatter than the back of the neck, having a small convex arc across its width. The measure of that arc is the fingerboard radius (also called fretboard radius).
Is Fingerboard Radius Important?
A few guitarists think that fingerboard radius has little to do with playability because one can barely feel the subtle convex arc variation. Some think that it has to do with playability and is completely subjective, depending on the players themselves. Some believe that it's important because a rounder radius is great for chords, and barre chords playing; while a flatter radius is great for single-note playing, and string bending across the fingerboard.
Different Types of Radius
For a long time since the inception of electric guitar, straight radius fretboards used a single radius down the entire length of the fretboard and still work as industry standard today. Some manufacturers invented compound radius fretboards recently and the radius changes along the length of the fingerboard, where the area closer to the nut is rounder, and closer to the body is flatter. They believe that it provides hand comfort for chords while allowing greater speed and cleaner string bending.
Common Sizes
Most classical guitars, banjos, and some acoustic guitars have flat fingerboards. The electric guitar is the only stringed instrument that offers multiple fretboard radius options. More recently, radii come in all sizes, for all manner of applications, especially custom guitars.
The most prevalent Fender radius is the modern 9.5” radius, which was adopted in the 1980s.The next most common Fender fingerboard radius, 7.25”, originated in the early 1950s. PRS guitars were mostly 10''. Gibsons had a 12'' radius ever since. In the 1980s, Ibanez, Charvel, and Jackson adopted a 16'' radius.