How to use the cat weight calculator
- Weigh your cat. The easy way: weigh yourself holding the cat, then subtract your own weight.
- Choose its body condition score (BCS) on the 9-point scale used in WSAVA’s charts:
- 5, ideal: ribs easy to feel, waist visible from above, small belly tuck
- 6–7, overweight: ribs harder to feel, waist hard to see
- 8–9, obese: ribs very hard to feel, no waist, belly fat
- Choose a weekly weight-loss pace between 0.5% and 2%.
- Read the estimated ideal weight, how much to lose, the weeks it should take and a starting calorie target.
The formula
Ideal weight ≈ current weight ÷ (1 + 0.10 × (BCS − 5))
This uses the common rule that each point above 5 on the 9-point scale is about 10% above ideal weight (the scale was validated for cats by Laflamme in 1997). It is an estimate, so ask your vet to confirm the target.
Weekly loss = current weight × pace (0.5–2%), from the AAHA 2014 Weight Management Guidelines.
Weeks to target = weight to lose ÷ weekly loss.
Starting calories for weight loss = 0.8 × RER at the ideal weight (AAHA 2021), where RER = 70 × (ideal weight in kg)^0.75.
Tips
- Weigh every 2–4 weeks and tell your vet how it is going.
- Never put a cat on a crash diet. Cats that stop eating can develop fatty liver disease (hepatic lipidosis) within days.
- Turn the calories into food with the cat food calculator.
- Unexplained weight loss in a cat that is not dieting needs a vet check.
Sources
- WSAVA Global Nutrition Committee: body condition score chart for cats (9-point scale).
- Laflamme D. (1997). Development and validation of a body condition score system for cats. Feline Practice 25: 13–18.
- AAHA (2014) Weight Management Guidelines for Dogs and Cats (0.5–2% per week for cats).
- AAHA (2021) Nutrition and Weight Management Guidelines for Dogs and Cats.
Frequently asked questions
How much should my cat weigh?
It depends on the cat’s frame and breed, so vets judge by body shape rather than a single number. At the ideal score (5 out of 9) you can feel the ribs easily under a thin fat layer and see a waist from above. This calculator estimates the ideal weight from your cat’s current weight and score.
How much should a cat weigh at 6 months?
There is no single target: breed, sex and frame make a big difference, and a large-breed kitten can weigh far more than a small one. Vets look for a steady weight gain and a good body shape at each check-up rather than a set number.
Is my cat overweight?
Probably, if you struggle to feel the ribs, cannot see a waist from above, or the belly hangs or bulges. On the 9-point body condition scale, 6–7 is overweight and 8–9 is obese. Each point above 5 is roughly 10% over the ideal weight.
How fast should a cat lose weight?
Slowly: 0.5–2% of body weight per week, according to the AAHA 2014 Weight Management Guidelines. For a 12 lb cat that is about 1 to 4 oz (30–110 g) a week. Fast weight loss can cause fatty liver disease in cats, so plan it with your vet.
How much should a kitten weigh by age?
Kittens should gain weight steadily every week, but the right weight depends on breed and sex. Weigh your kitten regularly on kitchen scales, keep a record, and bring it to vaccination visits so your vet can check the trend.