How this calculator works
The cited feline study reports a regression based on rib-cage circumference and the length between the patella and calcaneal tuber, both in centimetres. Small differences in landmark placement can change the estimate substantially. No human BMI thresholds are applied, and this page does not assign obesity categories or feeding targets.
Formula
Estimated body fat (%) = rib circumference (cm)/0.7062 - LIM (cm)/0.9156 - LIM (cm). The reverse modes rearrange this exact published expression.
Worked example
With a 40 cm rib circumference and 15 cm LIM, the expression gives approximately 25.2585% body fat. With 35 cm and 14 cm, it gives approximately 20.2705%. These are model estimates, not diagnoses.
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Frequently asked questions
Is this the human BMI formula?
No. Human BMI uses kilograms and metres squared. This feline morphometric equation estimates a body-fat percentage from two lengths.
Can I change feeding based on this result?
Discuss body condition, muscle condition and an appropriate target weight with your veterinarian before changing intake. A tape-measure estimate alone is insufficient.
Why was my measurement rejected?
Positive lengths can still be incompatible with the regression. Results outside physically possible body-fat percentages are rejected rather than clipped.