Utilisation Factor

Utilization factor gives us information how much area must be occupied by the standard cell. As we increase the utilization factor , total area of the chip or block will be decreased. Let us discuss how the total area decreases and total area was

Total Core Area = area occupied by macros+area occupied by standard cell+ empty area

UF  is defined as (area occupied by the standard cell)/(Total Core Are) and the UF is varied from .3 to .8 . In  industry mostly they will go with utilization factor of 0.7 -0.8

Assume that standard cell occupy 80mm area, all macros in the design occupy 30mm area

• Utilization Factor be 70% means in the core area there should be 30% of free space for future use.
  std. cell area =80mm
  All macros area = 30mm
  Free space area =35 mm
  Total Core Area= 80+30+35 =145mm
  
  And this explained properly in below figure.

• Utilization Factor be 80% means in the core area there should be 20% of free space for future use
  std. cell area =80mm
  All macros area = 30mm
  Free space area =20 mm
  Total Core Area= 80+30+20 = 130mm

we can observe that area of the core decreases if we increase the utilization factor of the block or design