Most artists use a scale of nine different shades of gray plus white and black, as you can see in the photo below, although there are some that use scales of 16 tones and even 30 but it is not frequent because It is also not necessary to do a good work.

Those of us with less experience usually use much smaller scales generally consisting of pure white, white with ¼ of black, white with ½ of black, white with y of black and pure black.

Said vulgarly: white (0), an intermediate tone at 50% between white and black (5) also called semitone, and two grays. One of them lighter (3) between white and halftone and another darker gray (7) between halftone and black. And with these five tones we are getting the best we can.