It depends on the rating. All glass used in fire-rated doors must be listed glass and be either ¾” wire or other listed material. Basic guidelines:
20 minute fire-rated door – 1,296 sq. in. per lite
3/4 hour fire-rated door – 1,296 sq. in. per lite
1-1/2 hour fire-rated door – 100 sq. in. per lite
3-hour flush door, no glass – per manuf. requirements​