Why pet kcal needs aren’t linear with body weight
Larger animals burn fewer calories per kg than smaller ones — a 40 kg dog doesn’t need eight times the calories of a 5 kg dog. Kleiber’s law (1932) sets metabolic rate proportional to body mass to the 0.75 power, which is the basis of the WSAVA formula and most professional veterinary nutrition references. Calculators that just multiply body weight by a flat “kcal/kg” figure systematically over-feed small pets and under-feed large ones.
Life-stage factors do most of the work
The same 5 kg cat needs 200 kcal/day if it’s a neutered indoor adult, but 350 kcal if it’s a growing kitten and 600 kcal if it’s lactating. Activity-level and reproductive-status adjustments to the RER baseline produce the daily target. Common mistakes: continuing “kitten” or “puppy” formulas past the recommended age, and not adjusting downward after spay/neuter.
Always check the bag
Energy density (kcal per cup or per gram) varies 2× across brands. A 5 kg cat needing 200 kcal/day will eat 50 g of a dense kitten food but 80 g of a low-density senior food. Read the “metabolisable energy” (ME) figure on the bag and weigh portions on a kitchen scale at least once — measuring cups are notoriously inaccurate (60–80 % measurement variance in Banfield studies).