That is a good weight for that age. We got our first chins last summer and we are up to 18 now. I have been keeping a monthly weight chart for each one. Of the females that were under 3 months of age when we got them, their weights at 3 months ranged from 300 grams to 452 grams. A lot depends on color too; some of the mutations like ebony, sapphire, and violet may develop more slowly. Our violet was only 300 grams at 3 months and our ebony was only 325 grams at 3 months. Both were over 500 grams by 6 months of age.