Hi Tony,
Fretboard radius: The radius of the fretboard refers to the curvature of the guitar neck. A flatter radius can make it easier to grab chords and move across the frets faster…
And,
The fingerboard radius is an important aspect of the guitar, as it greatly affects the ease of playing. But, the radius is only one element in the sum of the parts. There is also the width of the neck, the neck profile, the type of wood used on the fingerboard, the type of frets and the finish. Every aspect of the neck is blog-worthy, but we especially want to advise beginners to try out as many guitars as possible. So don’t lose yourself in all the underlying theoretical aspects! Does the guitar feel good? Then it’s okay… Source: Bax shop
I agree with Rogier. There are a lot of pieces to how your hand fits the neck of a guitar and if you are one to be particular about it, the best thing to do is try a bunch of guitars and see what you like.
My impression is that fretboard radius has more to do with what you are doing on the fretboard than sizing for your hand. The more curved allows easier cords and barres, the flatter more note articulation and individual note speed. Classical fretboards are flat for a reason.
For hand “fit”, you want to think of nut width and string spacing, scale of the guitar and neck profile (girth and shape cross section).
Keep in mind that there is no absolute need for smaller necks for smaller hands and visa versa. There are plenty of tiny handed classical players with full 52mm nuts and plenty of big ol’ ham handed rockers playing those skinny necked Ibanez guitars.
Find what fits you, or be adaptable. My hands are small average perhaps and I prefer the wider nuts (I play 46mm-52mm and dislike anything smaller). It is not about my hand size, it is what I like better for whatever reason even I can’t tell you. Yes, it is hard to do any thumb over stuff, but I can work around that.
