"Radius" is an English word that means "ray" in French. The "radius" therefore corresponds to the radius of a circle of which the fingerboard (the part of the neck on which guitarists place their fingers) is a part.
It is one of the measurements of an electric guitar's neck. The radius should not be confused with the neck profile. The profile is most often expressed by a letter representing a shape ("C," "D," "V") and corresponds to the back of the neck, which fits in the palm of your hand. The radius measures the shape of the fingerboard, on which the guitarist places their fingers. This radius is most often measured in inches because it appeared with the first folk guitars in the United States. Japanese and European brands use the metric system.
The image clearly shows that the key is a portion of the circumference of a circle whose diameter is more or less large
The difference in roundness is very clear between the vintage neck on the left and the modern one on the right.
There are several different radius sizes, ranging from approximately 7.25 to 20 inches. The radius affects playing comfort. It also influences bridge setup, particularly for guitars with height-adjustable saddles. For example, the Stratocaster and Telecaster have bridges with height-adjustable saddles.
Generally speaking, the larger the radius, between 16 and 20 inches, the more modern the guitar. The fingerboard is flat and allows for fast playing. Indeed, the radius, as well as the profile, width, and thickness, influences playing comfort. The smaller the radius, the more rounded the fingerboard: this is very likely a vintage guitar.
Should you take the radius into account when changing the pickups on your favorite guitar? The answer is in this article.
Each brand has its own preferred fretboard radius, depending on the era. In the 1950s, Fender generally equipped its guitars with a 7.25" radius fretboard, approximately 184mm, which was very round. This evolved in the 1960s with a 9.5" radius fretboard (241mm). This fretboard radius is still widely used by Fender today, even though it has a very vintage feel.
The most modern models from the Corona-based brand are equipped with fingerboards featuring a compound radius. This means they vary, for example, from 10 inches (254mm) near the nut to 14 inches (355mm) near the pickups . Gibson, on the other hand, to mention only the most well-known brands, most often uses a 12-inch radius (304.8mm to be precise). This choice by the Memphis brand is perhaps explained by the use of a "Tune-o-matic" or TOM bridge, whose saddles are not height-adjustable. Similarly, the bridge curvature is fixed, set to the 12-inch radius used for the fingerboard.
