You don't need a scale to assess whether your cat or dog is a healthy weight. You just have to refer to your hand.
For ideal weight, the palpation sensation of your animal's ribs and spine should be the same as when you palpate the bones with the back of your hand.
Your pet is overweight if palpation is similar to the bulging part of the inside of your hand. In that case, you must take measures to help him lose the excess pounds to avoid health problems related to obesity such as diabetes, joint problems, etc. Consult your veterinary team for specific recommendations for your animal.
Your pet is skinny if the feel of their bones compares to that of the top of your knuckles, where the bones come out with no layer of fat covering them. A consultation with your veterinarian is then advised in order to diagnose the reason for his thinness: under nutrition, metabolic problem, etc.
Geneviève
Animal health technician
(translated by Johanne)