The radius of a guitar fretboard refers to the curvature of the board and contributes greatly to the playability of a guitar. A small radius, like that found on a vintage Fender, feels great in the first couple of positions but notes tend to fret out when bending at higher positions. Many classical guitars have either flat or nearly flat fretboards (along with wide necks) that can feel cumbersome to players accustomed to most electric guitars. Most players seem to like something in between (e.g., 10" or 12").
Below you will find a reference guide to common fretboard radii -- I'll try to keep updating this over time. You'll notice that some companies like to use the same radius on most of their guitars (e.g., Fender) whereas others use a wide variety (e.g., Guild). Some companies offer custom builds with a variety of radius options (e.g., Carvin offers 12, 14, 16, and 20). The best of both worlds, perhaps, are compound radius fretboards from companies such as Parker.
Also interesting is that people buy relic Fender guitars with the vintage-correct 7.25" radius but don't realize that a 50 year old Strat or Tele that has been re-fretted a few times will have had its radius enlarged due to the sanding of the fretboard during the re-fret process. So, after a couple of these re-frets the actual radius of an old Fender is more like 10" or 12" (this is why the Eric Johnson signature model has a flatter, 12" fretboard radius).
7.25 Vintage Fender
9.45 Guild M-75 Aristocrat
9.50 Modern Fender; Guild X-175 Manhattan
10.0 PRS; Ibanez Joe Satriani; Guild X-500
11.5 PRS Santana
12.0 Gretsch White Penguin; most G&L; vintage Gibson Les Paul;
Guild S-100 Polara;
Fender Eric Johnson;
14.0 Suhr Modern Satin; Carvin DC-400
16.0 Jackson; Martin; Guild acoustics
16.5 Heartfield EX1 and EX2
16.92 Ibanez RG
17.0 Music Man JP15, Music Man Majesty
20.0 Carvin Alan Holdsworth model
Flat classical nylon string guitars; Vigier Excalibur Shawn Lane model
Compound or Conical Radius
9-12 Suhr Classic
10-13 Parker NiteFly
10-14 Suhr Modern
10-16 Warmoth; some recent Gibson Les Paul models
12-16 Charvel Guthrie Govan; Charvel San Dimas Pro Mod
Below you will find a reference guide to common fretboard radii -- I'll try to keep updating this over time. You'll notice that some companies like to use the same radius on most of their guitars (e.g., Fender) whereas others use a wide variety (e.g., Guild). Some companies offer custom builds with a variety of radius options (e.g., Carvin offers 12, 14, 16, and 20). The best of both worlds, perhaps, are compound radius fretboards from companies such as Parker.
Also interesting is that people buy relic Fender guitars with the vintage-correct 7.25" radius but don't realize that a 50 year old Strat or Tele that has been re-fretted a few times will have had its radius enlarged due to the sanding of the fretboard during the re-fret process. So, after a couple of these re-frets the actual radius of an old Fender is more like 10" or 12" (this is why the Eric Johnson signature model has a flatter, 12" fretboard radius).
7.25 Vintage Fender
9.45 Guild M-75 Aristocrat
9.50 Modern Fender; Guild X-175 Manhattan
10.0 PRS; Ibanez Joe Satriani; Guild X-500
11.5 PRS Santana
12.0 Gretsch White Penguin; most G&L; vintage Gibson Les Paul;
Guild S-100 Polara;
Fender Eric Johnson;
14.0 Suhr Modern Satin; Carvin DC-400
16.0 Jackson; Martin; Guild acoustics
16.5 Heartfield EX1 and EX2
16.92 Ibanez RG
17.0 Music Man JP15, Music Man Majesty
20.0 Carvin Alan Holdsworth model
Flat classical nylon string guitars; Vigier Excalibur Shawn Lane model
Compound or Conical Radius
9-12 Suhr Classic
10-13 Parker NiteFly
10-14 Suhr Modern
10-16 Warmoth; some recent Gibson Les Paul models
12-16 Charvel Guthrie Govan; Charvel San Dimas Pro Mod