Cat BMI Calculator

How to use this calculator

1. Measure around the rib cage near the ninth rib with the cat standing naturally.
2. With the cat standing, measure the left hind leg from the patella (knee) to the calcaneal tuber (hock), not the whole leg or foot.
3. Select the unit for each measurement and check the estimate against a hands-on body-condition assessment.

Formula and method

For the assumptions behind these results, read the explanation below. You can also explore Cat Age and Cat Calorie.

This is different from human BMI

Human BMI combines weight and height. This feline method instead compares two body measurements to estimate a body-fat percentage. It should therefore not be interpreted using human BMI cutoffs. The constants in the equation require centimeters, which is why the calculator converts inch inputs before applying the formula.

Measurement placement matters. Measuring the whole hind leg instead of the knee-to-ankle segment can produce a misleading or negative answer. Thick fur, a tense stance, or pulling a tape too tightly can also alter the circumference. Repeat a measurement rather than relying on a single hurried reading.

Interpret the range with care

The published method describes estimates above 10% and below 30% as non-obese, and estimates of 30% or more as warranting clinical assessment for excess body fat. Values of 10% or less fall outside that stated non-obese interval; the number alone does not diagnose underweight. A body-condition score and examination remain necessary.

Track consistent measurements if using the tool to observe change, but do not turn the number into a diet prescription. Cats should not be starved or placed on abrupt crash diets. Unexpected weight loss or gain deserves a discussion with a veterinarian, especially when appetite, thirst, or activity also changes.