Rattitz Saga: Gohan was 1-1327, when his dad was in trouble.
Saiyans Saga: He was in between 1100 and 12000. He would only get to 12000 when he was really angry.
Frieza Saga: Gohan's powerlevel before powerup by Guru was 14000. After powerup it was 24000.
Cell Saga: After training with his dad in the Hyperbolic Time Chamber he was at 20,000,000. After turning SSJ 2 he was at 35,000,000.