The Feline Body Mass Index follows the same concept as the human BMI measurement where you look at a person's weight and height and work out the percentage of body mass made up of fat.
Measurements You Need to Calculate Your Cat's FBMI
While your cat is in a standing position, with the legs perpendicular to the ground and the head upright (good luck with that!):
Measure the circumference of your cat’s rib cage. (The level of the 9th rib is ideal.)
Now measure the length of the lower back leg from the knee to the ankle and write down both numbers, because with what is coming, you probably won’t remember them.
Calculating the FBMI
Divide the rib cage measurement by 0.7062 and subtract the length of the leg.
Divide that answer by 0.9156.
Subtract the leg length from that number, and that is your cat’s BMI.
Prefer not to use this formula? Follow the following rule of thumb:
If you can't feel your cat's ribs when you run your hand down her chest, she likely needs to lose a pound or two.
Some other tips for managing your cat's weight:
Feed high-quality food
Limit free feedings
It's hard keeping an indoor cat trim but definitely worth the effort.