Cat BMI Calculator

Created by Michael Darcy
Reviewed by Hanna Pamuła, PhD candidate and Jack Bowater
Last updated: Apr 06, 2022

Cats are known to be fluffy, so it may be difficult to tell when there is a little bit too much of your pet friend to love. Weighing your pet is not enough - a healthy cat weight depends on many factors such as its breed, age, sex... Our cat BMI calculator is designed to save you the hassle and answer the burning question "is my cat overweight?" regardless of those. All you need to do is take two measurements!

Unfortunately, obesity is becoming more and more common amongst domestic cats. Of course, it is difficult to resist our fluffy friends, especially when they ask for a snack, so we may end up overfeeding them. If that happens to be the case, do not worry - in this article, you will find tips on how to help your cat lose weight!

How to take measurements for the cat BMI calculator?

The cat BMI calculator is based on the Feline Body Mass Index, which estimates your cat's body's fat content based on its proportions. It is simple and requires only two measurements. To use it, follow these instructions:

  1. Make sure your cat is standing with its head in the upright position.
  2. Measure your cat's rib cage. Ideally, you want to do this at the 9th rib level, located by the cat's front legs.
  3. Measure the length of your cat's lower back leg from the knee to the ankle.
  4. Input measured values into the cat BMI calculator. The result will be found using the following formula:

FBMI = (((rib cage/0.7062) - leg length )/0.9156) - leg length.

In fact, to make using our cat weight calculator easier, we have prepared a picture illustrating how to take the measurements:

Image of a cat with measuring guides going a) around the 9th rib and from and b) from the knee to the ankle of the lower back's leg

What does the result mean? FBMI ranges

Although there are five BMI ranges for humans, it was reduced to four for cats. Below, we present the FBMI chart.

FBMI Interpretation
<15 Underweight
15-29.9 Normal weight
30-42 Overweight
>42 Obese

To clarify it more, let's use an example. If we consider a cat with a rib cage circumference of 14 inches and a lower back leg of 2 inches, its FBMI is 44.4. Now, if we can change the FBMI value to 29 in the calculator, which is in the healthy weight range, the tool will show us that that the target rib cage circumference is approximately 10 inches.

Comparing your result from the calculator with this table will allow you to answer the question posed at the beginning: "Is my cat overweight?" But what to do if the answer is "Yes?"

How to help your cat lose weight?

Similarly to humans, maintaining a healthy cat weight helps prevent against several health issues. Once you've decided to take action, you can use this cat weight calculator to check your cat's progress and see how far they have to go to reach the healthy range. With that being said, here are some things that you can do to help your kitten:

  • Cut back on treats. Most cats will also appreciate other rewards, including playtime with you!
  • If you would rather keep the treats, slightly reduce the amount of normal food. However, never starve your cat. "Crash diets" do not work well for both humans and pets. If you were a cat you wouldn't enjoy this, would you?
  • Replace dry food with canned, which tends to have higher carbohydrate and protein content. This will keep your cat fuller for longer. It will also prevent grazing - dry food to cats can be just what chips (or other snacks) are to us!
  • Play with your cat. You can think of it as a pleasant exercise for your fluffy friend and a way to burn excess calories.
  • If you have two cats (or more), you may have to feed the overweight one in a separate room or keep the healthy-weight cat's food in a place out of the bigger cat's reach.

Bear in mind that this is just a guide. There may be various causes of excessive weight, so always make sure to consult your vet to rule out more severe conditions. You may also check your cat's calorie intake to get an idea how much food it needs. It may be difficult to keep cats trim, especially if they prefer to stay indoors, but it's definitely worth the effort!

Michael Darcy
Rib cage circumference
Length of the lower back leg
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