Cat BMI Calculator

Why cats are scored on a 9-point scale instead of a BMI

Body mass index compares weight to height squared, and it works for people because adult human height stops changing at a predictable age and human frames sit inside a narrow range. A cat has neither advantage. A healthy Singapura can weigh 6 pounds and a healthy Maine Coon can weigh 20, and both can be at the same body fat percentage. Fur makes the problem worse, since a long coat can hide two pounds of fat or make a lean cat look round. A formula built on height would call a big-boned Maine Coon obese and a fat Siamese normal.

Veterinarians score body fat directly instead, by hand and by eye. The standard is the 9-point body condition score published by the World Small Animal Veterinary Association, whose cat body condition chart is the version most clinics print. The same scale is carried into the American Animal Hospital Association (AAHA) weight management guidelines. On the 9-point cat chart, 1 is emaciated, 5 is ideal and 9 is obese. Scores 4 and 5 both count as ideal, with 4 on the lean side. The WSAVA chart notes that a 6 may be acceptable in some cats, especially older ones, because a small reserve is not the same thing as obesity.

That is why this page asks for a score and a weight rather than a height. The score tells you how much fat the cat carries. The weight tells you how many pounds that fat adds up to. Put together, they give an ideal weight you can aim at.

What each body condition score looks and feels like

Run your hands along the cat's sides and back, then look at the animal from above and from the side. Three landmarks carry most of the information: the ribs, the waist behind the ribs, and the abdominal tuck where the belly rises toward the hind legs.

The jump from 6 to 7 is the one owners miss. At 6 the cat still looks fine in a photograph, and the waist is there if you look for it. By 7 the waist has filled in and the belly hangs. Photographs hide the change because the cat is seen from the same angle every day, which is why the hands matter more than the camera.

Turning a score into an ideal weight

The AAHA 2014 weight management guidelines give a working rule: on the 9-point scale, each point above 5 is equivalent to being about 10% over ideal body weight. That makes the arithmetic short. Divide the current weight by one plus the excess fraction.

• Score 6: divide by 1.10
• Score 7: divide by 1.20
• Score 8: divide by 1.30
• Score 9: divide by 1.40

Take a 14-pound cat scored 8 of 9. The excess is 30%, so the ideal weight is 14.0 divided by 1.30, which is 10.8 pounds. The cat is carrying about 3.2 pounds of fat, and that is roughly 23% of its current body weight. On a 10-pound frame, three pounds is not a cosmetic problem.

Two caveats keep the number honest. First, the rule assumes the cat is a normal adult with normal muscle. A senior cat that has lost muscle but gained fat can score 6 while weighing less than it did at 5, and the formula will understate the fat. Ask the vet to score muscle condition separately. Second, the estimate is a starting point for a weight-loss plan, not a target to chase week by week. Your vet may adjust it once the cat is on a measured diet and the scale starts moving.

How to score your own cat in two minutes

Stand behind the cat while it stands on all fours, and use flat fingers rather than fingertips. Fingertips feel every rib on every cat and will talk you into a score that is too low.

• Ribs. Press gently along both sides of the chest. You should feel the ribs under a thin layer of fat, the way you feel the bones on the back of your hand. If you have to press to find them, the cat is at 7 or higher. If they are sharp and bare, the cat is at 3 or lower.
• Waist. Look straight down from above. A cat at 5 has an hourglass behind the rib cage. A straight line from shoulder to hip is a 7. A bulge is an 8 or 9.
• Tuck. Look from the side at belly level. The belly should rise from the ribs toward the hind legs. A belly that hangs level or sags is a fat pad.
• Spine and hips. At 5 the spine feels like a row of small bumps under a little padding. Bones that stand out mean underweight.

Long-haired cats need the hands more than the eyes, because the coat hides the waist completely. Compare what you feel to the WSAVA chart rather than to the cat next door. Two cats of the same weight can be four points apart, and the score is what the vet will act on.

Why the extra pounds matter: joints and diabetes

Fat tissue is not storage. It releases hormones and inflammatory signals, and in cats that changes the risk profile for several diseases. The AAHA guidelines list diabetes, orthopedic disease, skin disorders, respiratory problems and some cancers among the conditions linked to excess weight, and the FDA summary of those guidelines covers the same list for pet owners. Peer-reviewed reviews put the share of US cats that are overweight or obese at close to 40%, which makes this the most common nutritional problem in the species.

The joint story is the one owners notice first. A cat that stops jumping onto the bed is often read as "getting older" when the real change is three extra pounds on two small knees. The diabetes story is the one that costs the most. A cat on twice-daily insulin needs a syringe every 12 hours, a glucose curve at the vet, and a owner who can be home on schedule.

A safe plan to bring the weight down

The AAHA 2014 guidelines set the target rate at 0.5% to 2% of body weight per week for cats. For a 14-pound cat that is roughly 1.1 to 4.5 ounces a week, or about 0.4 to 1.8 pounds a month. Faster loss is dangerous in this species. A cat that stops eating or crashes can develop hepatic lipidosis, a fatty liver condition that is often fatal without tube feeding, so a slow plan is the safe plan.

What works in practice:

• Measure the food. Free feeding is the usual cause. Weigh the daily ration on a kitchen scale in grams, because a scoop varies by 20% from one day to the next.
• Feed to the target weight, not the current weight. The calorie target should be set from the ideal weight, and your vet can calculate it from resting energy requirement.
• Split the ration into several meals. Four small meals beat one large one for a cat that begs.
• Use a food made for weight loss. Reducing portions of a regular diet cuts protein along with calories, and cats need protein to keep muscle.
• Weigh weekly on the same scale. A baby scale works well. Log the number, because the trend is what matters.
• Add play, not stress. Two short sessions with a wand toy burn calories and give the cat something to do besides waiting for food.

Expect a plateau around weeks 4 to 6. It is normal, and it is the point where portions usually drift back up.

What common weights mean at each score

This table applies the AAHA rule to weights owners see often. Read across the row for your cat's current weight to find the ideal weight at each score. The numbers are estimates, and a vet visit will refine them.

A 16-pound cat scored 7 carries about 2.7 pounds of excess fat. That is more than most owners guess when they lift the cat, because the weight is spread over a small body and the coat smooths the outline. The same 2.7 pounds on a person of average height would be a rounding error, which is why the score matters more than the scale alone.

When to call your vet instead of using a calculator

This tool estimates a target from a score you assign at home. Several situations need a veterinarian rather than an estimate.

• The cat is losing weight without a diet. Unexplained loss can point to thyroid disease, kidney disease, diabetes or cancer, and none of those are fixed by feeding more.
• The score is 3 or lower. Underweight cats need a medical workup, not a weight-gain plan invented online.
• The cat has lost muscle but kept its belly. That pattern suggests muscle wasting with fat gain, and the ideal-weight formula will mislead you.
• The cat stops eating for more than 24 hours during a diet. This is an emergency in cats because of the fatty liver risk.
• The cat is a senior. Cats over 12 often need more protein and a different calorie target, and about 15% of cats past that age are underweight rather than over.

Bring the score and the weight to the appointment. A vet who sees "8 of 9, 14 pounds, down from 14.6" has something to work with, and a body condition score recorded at every visit is the single best way to catch a drift before it becomes a diet. The WSAVA chart is the reference most clinics use, and the AAHA guidelines set the weight-loss targets your vet will follow.

This is an estimate for planning, not veterinary advice. Body condition scoring is a clinical skill, and a cat with a medical condition needs a diagnosis before a diet.