Body condition score (BCS)
A 1–9 (or 1–5) scoring system vets use to assess whether a pet is the right weight. More useful than the scale because it accounts for build and muscle.
Body condition score (BCS) describes body fat. On the 9-point scale (most common), 4–5 is ideal, 6–7 is overweight, 8–9 is obese, 1–3 is underweight. On the 5-point scale, 3 is ideal.
How to check at home: ribs should be easily palpable through a thin layer of fat (like feeling the back of your knuckles, not your wrist), a visible waist when viewed from above, and a slight tuck-up to the abdomen when viewed from the side. The "cat belly pouch" (primordial pouch) is normal and does not count toward score.
BCS matters because it is the single best predictor of lifespan and chronic disease in pets. A landmark 14-year Labrador study showed lean-fed dogs lived 1.8 years longer than free-fed siblings — and avoided arthritis, diabetes, and many cancers along the way.
Combine BCS with muscle condition score (MCS) in seniors — older pets often gain fat while losing muscle, which a single weight does not catch.