Is my female rottie is under-weight?

karthick here owing 8 month female rottie weight just 25-30 not an accurate weight just an approxiamate im feeding quality(Max and Pedigree these are the feed available in my home town) coming month im going to feed her ROYAL CANIN prescribed for rottie puppy) food upon my knowledge...I want to know whether its d correct weight for her age???? I feel its the under-weight for her....Rottie is my first dog and im an expert in dogs....Pls can anyone say and guide me ....Waiting for everyone's answers pls...............