Technically there is NO precise conversion between Turns and KV. KV indicates no load performance while Turns describes the “structure” or “construction” of the motor. Seems like Turns is still the most tried and proven system of performance measurement even though KV rating can still be used for determining what motors are in an approximate range.
Generally a lower KV rating means more torque but less speed. For example, the Fazer VE-X comes witha 2700KV motor, which is intended for starters only.
4T is considered VERY FAST. For beginners, 13.5T would probably be safer.
The information below shows an approximate equivalence of T rating VS KV rating:

