Weigh the cat once a week, at the same hour, on the same scale, before the first meal. A baby scale reads to 10 or 20 g, and the difference method on a human scale holds to about 50 g if you repeat it 3 times. Either way, the number that matters is not today's weight but the 10 percent change over 3 months, because a cat can lose 400 g and still jump on the counter.
Weight is the cheapest test in cat care and the one owners skip most. A 5 kg cat that drops to 4.7 kg has lost 6 percent and shows nothing at the bowl; the same cat at 4.2 kg has lost 16 percent and is now a workup.
Two methods, one precision target
| Method | Precision | You need | Main error source |
|---|---|---|---|
| Baby scale, cat alone | plus or minus 10 to 20 g | Flat digital baby scale, 30 to 40 dollars | Cat steps off before the read locks |
| Human scale, difference | plus or minus 50 g | Digital bathroom scale, 3 readings | Your own weight shifts 300 g by evening |
| Luggage scale plus sling | plus or minus 50 to 100 g | Hook scale, cloth bag with 4 handles | Cat twists and the bag swings |
| Vet clinic scale | plus or minus 5 to 10 g | Appointment, 1 per 3 months | Only 4 numbers a year |
Anything finer than 20 g is wasted at home: a cat's weight swings 50 to 100 g across a day from water, food, and litter box timing. Method matters less than repeating the same method every time.
Four conditions that must never change
Same scale, same hour, same room, same state of fill. Pick a time 20 to 30 minutes after the cat wakes and before breakfast, after the litter box if you can arrange it. Weigh before food and after urination, and take the collar off, since a collar and tag run 15 to 25 g. A cat weighed at 7 a.m. unfed and the same cat at 9 p.m. after dinner are 100 to 150 g apart, which is 3 percent of a 4 kg cat and enough to fake a trend.
Direct method: 4 steps
Put the scale on a hard floor, not carpet, and zero it, in a quiet corner the cat already uses rather than a bathroom with a closing door. Place a 40 by 50 cm towel or a shallow box on the scale, press tare, and let the cat investigate for 30 seconds with a treat. Set the cat down with the front paws first and keep one hand cupped near the chest without holding. Read the display once it stops blinking, then repeat twice; if the 3 readings spread more than 30 g, take the middle one and try again tomorrow.
A cat that will not stay still can be weighed in a carrier: weigh the carrier empty, then with the cat, and subtract. Carrier weight is stable to 5 g, so this keeps precision near 20 g.
Difference method: the arithmetic
Weigh yourself alone, then with the cat held against your chest, both times on the same scale, and subtract. If you are 62.0 kg and the pair reads 66.8 kg, the cat is 4.8 kg. Do it 3 times and average: on a 0.1 kg display, 3 readings of 66.8, 66.9, and 66.7 kg put the cat at 4.8 kg plus or minus 50 g. Weigh yourself first, because your own body loses 300 to 500 g of water during a normal afternoon, and that error lands entirely on the cat.
What a change means
Normal week to week drift is 1 to 2 percent, so 45 to 90 g on a 4.5 kg cat: ignore it. A 5 percent drop in 30 days, about 225 g, is a reason to book a non-urgent visit with a weight history in hand. A 10 percent drop in 3 months, 450 g on the same cat, is the threshold most vets treat as a workup trigger: blood panel, thyroid, kidney values, and a dental check. On the gain side, 10 percent in 8 weeks, 450 g, pushes a cat from ideal into overweight, and the fix is 10 percent fewer calories, not a diet started overnight.
Small cats are less forgiving. On a 3 kg cat, 300 g is 10 percent; on a 6 kg cat it is 5 percent. That is why you compare percentages, never raw grams between 2 cats.
Weight is not the whole picture
Body condition score (BCS) runs 1 to 9, with 5 ideal. A cat can hold 4.5 kg while losing 200 g of muscle and gaining 200 g of fat, and the scale will not move. Run a hand along the spine every 2 weeks: ribs felt with light pressure at BCS 5, invisible at BCS 7, and a 1 cm fat layer over the hips at BCS 8. Weighing monthly plus a BCS check every 2 weeks catches what either one alone misses.
A log you can actually keep
| Week | Date | Weight (g) | Change (g) | Change (%) |
|---|---|---|---|---|
| 1 | 03-02 | 4520 | baseline | 0.0 |
| 2 | 03-09 | 4495 | -25 | -0.6 |
| 3 | 03-16 | 4430 | -65 | -1.4 |
| 4 | 03-23 | 4402 | -28 | -0.6 |
| 5 | 03-30 | 4310 | -92 | -2.1 |
Five rows in a phone note beat a perfect spreadsheet you stop filling in. Add 2 columns by hand if you like: appetite out of 5, and water intake in ml, and keep the file with the vaccination dates. A cat that eats 5 out of 5 and still loses 2 percent a week for 5 weeks needs bloodwork, not a new food.
Five steps for the first weigh-in
- Choose the scale today and write the model on the log, so the number stays comparable.
- Fix the slot: 20 to 30 minutes after waking, before food, after the litter box.
- Take 3 readings and log the middle one, plus the date and the time.
- Weigh weekly for 8 weeks, then monthly if the trend is flat within 1 percent.
- Flag any 5 percent drop in 30 days or 10 percent in 90 days, and bring the log to the visit.
Keep the scale where the cat already walks, near the food bowl, so the weekly routine costs 60 seconds and never becomes a chase.
Frequently asked
My bathroom scale only shows 0.1 kg. Is that precise enough?
Barely, and only with repeats. A 0.1 kg display gives 100 g steps, so take 3 weighings and average; that gets you to roughly plus or minus 50 g. For a cat under 4 kg, or for tracking a diet plan at 1 percent per week, a 30 to 40 dollar baby scale reading to 10 g is the better buy.
How often should I weigh a cat that is losing weight on purpose?
Every 7 days, same hour, same scale, and aim for 1 to 2 percent of body weight per week, which is 45 to 90 g on a 4.5 kg cat. Faster than 2 percent a week raises the risk of hepatic lipidosis, so if the cat drops 3 percent in 7 days, feed more and call the vet before continuing.
The weight is stable but my cat looks thinner. What is happening?
Muscle loss with fat gain, which is common in cats over 10 years and in untreated diabetes or hyperthyroidism. The scale cannot see the swap, so check body condition score every 2 weeks and feel the spine and hips. Ask for a blood panel including T4 and glucose if the ribs feel sharper at the same weight.