It is very important to keep our cat at an adequate weight. Unless your vet advises otherwise, you should try and keep your cat in the weight-range typical for his or her breed and gender.
Here we present a chart of the weight distribution for Siamese cats. The weight of a typical female ranges from 3.5kg to 4.8kg and that of a male from 4.5Kg to 5.5kg. That is, 7.7lbs to 10.6lbs for females and 9.9lbs to 12.1lbs for males.