Is there a BMI calculator for cats? There are calculators that give a number for a cat — usually weight divided by height squared, in the style of human BMI — but there is no standard pet BMI, and vets do not use one. What vets use is body condition score, or BCS: a 9-point scale, where 1 is very thin, 4 or 5 is ideal, and 9 is very fat, judged by feeling the ribs and looking at the waist. This guide explains what pet BMI calculators do, why they are not reliable, and how to check your cat's condition properly instead. Every figure is an estimate, not a diagnosis: if you are worried about your cat's weight, ask your vet. The cat body condition score chart gives the 9-point scale in full.
The short version is: do not trust a BMI number for your cat. A cat's healthy weight depends on its breed, its frame, its sex, and its muscle — and a single number cannot capture that. A muscular dog can have a high BMI and be perfectly healthy, while a fat dog of a different breed can have a normal BMI and be overweight. Feel the ribs, look at the waist, and give your cat a body condition score — that is what a vet does, and it is far more useful than any BMI. The is my cat overweight calculator guide helps you check your own cat's condition.
What pet BMI calculators do
A pet BMI calculator usually asks for your cat's weight and its height — often the height at the shoulder, or the length from nose to tail — and divides weight by height squared, in the style of human BMI. Some ask for the breed, and compare the result to a range for that breed. The result is a number, and the calculator tells you whether that number is low, normal, or high. The problem is that there is no standard for what that number should be: different calculators use different formulas, different heights, and different ranges, so the same cat can get a different answer from each one.
Human BMI works, roughly, because humans are all the same shape — two arms, two legs, and a fairly standard frame. Cats are not: a Dachshund and a Greyhound are both dogs, but they have completely different shapes, and a weight that is healthy for one is not healthy for the other. A muscular dog can weigh a lot and be lean, while a fat dog can weigh the same and be overweight. Height does not capture that, and neither does weight on its own. The cat ideal weight chart by size guide gives the ideal weight ranges by size, and the cat calorie calculator works out the daily calories for a cat of any weight.
Why vets use body condition score instead
Vets use body condition score, or BCS, because it judges the cat, not a number. BCS is a 9-point scale, where 1 is very thin, 4 or 5 is ideal, and 9 is very fat. At a score of 4 or 5, you can feel the ribs under a thin layer of fat, you can see a waist from above and from the side, and there is a small pad of fat on the belly. At a score of 6 or more, you cannot feel the ribs, there is no waist, and the belly hangs. At a score of 3 or less, you can see the ribs, the spine, and the hip bones, and there is no fat to feel.
| Score | Label | What you see and feel |
|---|---|---|
| 1 | Emaciated | Ribs, spine and hip bones are easy to see, even from a distance. No fat cover at all, and the waist is very obvious from above and from the side. |
| 2 | Very thin | Ribs are easy to see, and the waist and tummy tuck are very obvious. There is almost no fat to feel over the ribs. |
| 3 | Thin | Ribs are easy to feel and may be visible. The waist is obvious from above, and the tummy tuck is obvious from the side. |
| 4 | Ideal — lean end | Ribs are easy to feel under a thin layer of fat. The waist is easy to see from above, and the tummy tuck is visible from the side. |
| 5 | Ideal | Ribs are easy to feel under a thin layer of fat, with no fat to pinch. The waist is visible from above, and the tummy tuck is visible from the side. |
| 6 | Above ideal | Ribs are harder to feel — you have to press to find them. The waist is hard to see from above, and the tummy tuck is less obvious. |
| 7 | Overweight | Ribs are hard to feel under a clear layer of fat. The waist is hard to see from above, and the tummy tuck is gone from the side. |
| 8 | Very overweight | Ribs are very hard to feel. The waist is gone from above, and the belly is rounded or sagging from the side. |
| 9 | Obese | Ribs cannot be felt at all under a thick layer of fat. There is no waist from above, the belly is very rounded, and fat deposits are visible on the neck, limbs and chest. |
Use the table above to score your cat: look at it from above and from the side, feel its ribs and waist, and give it a score out of 9. A cat at a score of 4 or 5 is at a healthy weight, whatever the scales say. A cat at a score of 6 or more needs less food and more exercise; a cat at a score of 3 or less needs more food — or a vet check, if the loss is unexplained. The cat body condition score chart gives the 9-point scale in full, and the how to weigh your cat at home guide gives the weighing method.
How to check your cat's condition at home
Feel the ribs: run your hands along your cat's sides, with light pressure. You should be able to feel the ribs under a thin layer of fat, without pressing hard — like feeling the bones in the back of your hand. If you cannot feel the ribs at all, your cat is probably overweight. If you can see the ribs without touching, your cat is probably underweight. Look at the waist: from above, your cat should have a waist — a narrowing behind the ribs. From the side, the belly should tuck up behind the ribs, not hang down.
Do the check every month, and write the score down: a single score matters less than the line over months. A cat that is gaining condition steadily needs less food, a cat that is losing condition steadily needs more food — or a vet check, if the loss is unexplained. A cat that is at a score of 4 or 5, eating a measured amount, and exercised every day, is a cat that will live longer and feel better. The cat calorie calculator guide works out how much to feed, and the cat weight loss diet plan guide covers a cat that needs to lose weight.
What to do with a BMI result
If a BMI calculator has given you a number, do not act on it alone: check your cat's body condition score, weigh it, and compare the two. If the BMI says your cat is overweight but you can feel its ribs and see its waist, the BMI is probably wrong for your cat's breed and frame. If the BMI says your cat is normal but you cannot feel its ribs and there is no waist, your cat is probably overweight, whatever the BMI says. The body condition score is the better guide, and the vet's judgement is better still.
If your cat is at a body condition score of 6 or more, reduce the food by a tenth, increase the exercise, and re-check in a month. If it is at a score of 3 or less, increase the food by a tenth, and ask your vet if the loss is unexplained. If it is at a score of 4 or 5, keep doing what you are doing. A cat that is at a healthy weight, eating a measured amount, and exercised every day, is a cat that will live longer and feel better. The senior cat diet guide covers feeding in the senior years.
When to ask a vet about weight
Ask a vet if your cat is losing weight and you do not know why, if it is gaining weight on a measured amount of food, if it is at a body condition score of 3 or less or 7 or more, or if it has stopped eating. A cat that stops eating is an emergency: a cat that does not eat for more than a day or two can develop a serious liver problem, and a dog that stops eating needs checking too. A vet can work out whether the weight is a problem, and what to do about it.
Ask a vet, too, if your cat is a senior and is losing weight: weight loss in a senior cat can be a sign of kidney disease, thyroid disease, or cancer, and the earlier it is found, the better the chance of treating it. A vet who knows your cat will notice changes sooner, and will know what is normal for your individual cat. The cat lifespan estimator estimates a lifespan for any breed and size.
For related reading, see the cat body condition score chart, the is my cat overweight calculator guide, the cat ideal weight chart by size guide, the cat calorie calculator, the how to weigh your cat at home guide, the cat calorie calculator guide.
Frequently asked questions
Is there a BMI calculator for cats?
There are calculators that give a number — usually weight divided by height squared, in the style of human BMI — but there is no standard pet BMI, and vets do not use one. What vets use is body condition score, a 9-point scale judged by feeling the ribs and looking at the waist. Do not trust a BMI number for your cat on its own.
Why does pet BMI not work?
Human BMI works, roughly, because humans are all the same shape. Cats are not: a Dachshund and a Greyhound are both dogs, but they have completely different shapes, and a weight that is healthy for one is not healthy for the other. A muscular cat can weigh a lot and be lean, while a fat cat can weigh the same and be overweight. Height does not capture that.
What is body condition score?
Body condition score, or BCS, is a 9-point scale, where 1 is very thin, 4 or 5 is ideal, and 9 is very fat. At a score of 4 or 5, you can feel the ribs under a thin layer of fat, you can see a waist from above and from the side, and there is a small pad of fat on the belly. The table above gives the full scale.
How do I check my cat's condition at home?
Feel the ribs — you should be able to feel them under a thin layer of fat, without pressing hard. Look at the waist from above — there should be a narrowing behind the ribs. Look from the side — the belly should tuck up behind the ribs, not hang down. Do the check every month, and write the score down.
My cat's BMI says it is overweight, but it looks fine. What should I do?
Check its body condition score: if you can feel its ribs and see its waist, the BMI is probably wrong for your cat's breed and frame. If you cannot feel its ribs and there is no waist, your cat is probably overweight, whatever the BMI says. The body condition score is the better guide, and the vet's judgement is better still.
When should I ask a vet about my cat's weight?
Ask a vet if your cat is losing weight and you do not know why, if it is gaining weight on a measured amount of food, if it is at a body condition score of 3 or less or 7 or more, or if it has stopped eating. A vet can work out whether the weight is a problem, and what to do about it.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.