Designing Kitchens and Bathrooms - Range wire guage by code

hey got a new Ge Profile range. it's a 4 wire connection one, but according to the instructions it can be wired with 3 wire, but that's not the question here.

the old stove top was just a stove top sitting on the counter, no under (etc). so the counter top was cut off and we bought a conventional stove. but the question is, looking at the wire im not sure if the wire is the right gauge for the job (the wire coming out of the wall for the old stove (top only).

house was built about 10 years ago

q1) by code what should the wiring be for the wire coming from the breaker box for the new stove?

q2) is there some sort of gauge measurer? how can i tell the gauge of the wire coming out of the wall. (there are no marking on the wire, nothing written)

thanks for any help.

oh yeah, the instruction don't say what should be coming out of the wall, but under electrical requirements it says this:
" you must use az 3 wire single-phase a.c 208Y/120 volt or 240/120 volt, 60 hertz electrical system.

use only a 3-conductor or a 4 conductor UL-listed range cord.

a range cord rated at 40 amps with 125/250 minimum volt range is required. a 50 amp range cord is not recommended but if used, it should be marked for use with n ominal 1-3/8" diameter connection openings."

Modern ranges are more energy efficient that older units, so the older one was likely 50A. #8 is 40A, #6 is 50A. There are gauges available for checking the wire, try hardware and home stores. And you should use the proper plug. They are also labeled according to Amps. Newer appliances use 4 wire.