Cat BMI Calculator
Is your cat a healthy weight? This free cat BMI calculator finds your cat’s Feline Body Mass Index (FBMI) from two measurements, scores its body condition the way a vet does, estimates the ideal weight, and shows normal cat weight by breed (kg and lb) and by age.
How the Cat BMI Calculator Works
The five tools cover the Feline BMI, a Body Condition Score, an ideal-weight estimate, normal weight by breed, and a weight-by-age chart.
Cat BMI Chart (FBMI Ranges)
This cat BMI chart shows what each Feline Body Mass Index band means. FBMI roughly tracks body-fat percentage, so the categories line up with how much fat your cat is carrying.
| FBMI score | Category | Approx. body fat | What it means |
|---|---|---|---|
| Below 15 | Underweight | Under 15% | Ribs and spine easy to see or feel; check with a vet |
| 15–29.9 | Healthy / normal | 15–30% | Ideal — ribs felt under thin fat, visible waist |
| 30–42 | Overweight | 30–42% | Ribs hard to feel, waist fading; time to act |
| Above 42 | Obese | Over 42% | Heavy fat cover, no waist; vet-supervised plan |
How to Measure Your Cat’s Feline Body Mass Index
The FBMI needs just two measurements with a soft tape. First, the rib-cage circumference: with your cat standing, measure all the way around the chest just behind the front legs. Second, the lower-leg length (LIM): measure the back leg from the kneecap (patella) down to the ankle bone (hock). The calculator then applies the veterinary formula, FBMI = ((rib cage ÷ 0.70622) − leg) ÷ 0.9156 − leg, with both measurements in centimetres, to estimate the body-fat percentage. Take each measurement twice and average them, keep the tape snug but not tight, and do it when your cat is calm — small errors in the leg measurement move the score the most.
Body Condition Score: The Vet Gold Standard
Most veterinarians judge weight with the Body Condition Score (BCS), a 9-point scale where 4 to 5 is ideal, rather than any single number. It relies on three hands-on checks you can do at home. Ribs: you should be able to feel them easily under a thin layer of fat, without pressing hard and without seeing them stick out. Waist: looking down from above, a healthy cat has a visible hourglass behind the ribs. Profile: from the side, the belly should tuck up slightly rather than sag or bulge. Each point above 5 represents roughly 10% over ideal weight, so a BCS of 7 is about 20% overweight. The Body Condition tab turns these three checks into a score and tells you what to do next.
Normal Cat Weight by Breed (kg & lb)
“Normal” weight depends heavily on breed and sex — a petite Singapura and a giant Maine Coon are both healthy at wildly different weights. Males usually run heavier than females of the same breed. The table shows typical healthy adult ranges; use the By Breed tab for a male/female figure.
| Breed | Healthy weight (kg) | Healthy weight (lb) | Notes |
|---|---|---|---|
| Domestic shorthair | 3.6–4.5 kg | 8–10 lb | The typical house cat |
| Siamese | 2.7–4.5 kg | 6–10 lb | Slender, fine-boned |
| Persian | 3.2–5.4 kg | 7–12 lb | Stocky, dense coat |
| Bengal | 3.6–6.8 kg | 8–15 lb | Muscular, athletic |
| British Shorthair | 4.0–7.7 kg | 9–17 lb | Cobby and heavy-boned |
| Ragdoll | 4.5–9.1 kg | 10–20 lb | Large, slow to mature |
| Maine Coon | 5.9–8.2 kg | 13–18 lb | Largest domestic breed |
Cat Weight Chart by Age
Kittens gain weight fast — roughly a pound (about 0.45 kg) a month until around five months — then growth slows as they approach their adult size by about one year. This chart shows the average weight at each age for a domestic cat.
| Age | Average weight | In pounds |
|---|---|---|
| 8 weeks | ~0.9 kg | ~2 lb |
| 3 months | ~1.4 kg | ~3 lb |
| 4 months | ~1.9 kg | ~4 lb |
| 6 months | ~2.7 kg | ~6 lb |
| 9 months | ~3.3 kg | ~7 lb |
| 12 months (adult) | ~3.6–4.5 kg | ~8–10 lb |
How to Help an Overweight Cat Lose Weight Safely
If the calculator flags your cat as overweight, the fix is slow and steady. Set a target with the Ideal Weight tab, then trim daily calories by about 10 to 20% — measuring food by the gram, feeding a higher-protein or vet weight-loss diet, and cutting treats. Aim to lose no more than 0.5 to 2% of body weight per week. This matters enormously: cats that lose weight too fast can develop hepatic lipidosis (fatty liver disease), which is life-threatening, so never crash-diet a cat. Weigh every one to two weeks on the same scale, add short play sessions, and recheck the Body Condition Score monthly. A loss of even 5–10% of body weight can noticeably improve an overweight cat’s mobility and health.
Frequently Asked Questions
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