For an IT company, it is important to have enough spacing to mount a Dell or Lenovo server. The racks we use are about 29.5 inches or about 75cm from the front cage nut holes to the back ones.
If you are offering enclosed racks, be sure to allow 6-8 inches or 15-20cm behind the rear cage nuts for cable management arms and such. Enclosed racks should have at least one side with zero U space in back for vertical power distribution.