Body Condition Scoring (BCS) is a convenient way to answer the question, "Is my pet overweight?" In many ways, BCS is more meaningful than the number of pounds they weigh.
For my cats, I gauge their body condition by the 'roundness' of their shape and the size of the little belly that flaps back-and-forth when they run (this is properly called the inguinal fat pad).
For dogs, I check the 'jiggle' over their shoulders and if their body shape is more of a sausage or an hourglass.
See Purina's BCS chart below to rate your dog or cat. In the clinic, we also evaluate pets' muscle mass- this often improves along with BCS when pets switch to a more species-appropriate nutritious diet.