British Shorthair adults land in a 4.0 to 7.0 kg band, and the number that matters is not the breed average but 3 lines drawn on your own cat: 4.0 kg, 5.5 kg, and 7.0 kg. Weigh once a month on the same scale, log grams, and read the trend rather than the single number. A cat holding 5.2 kg for 6 months is stable; a cat that moved from 4.8 to 5.4 kg in 8 weeks is gaining 75 g a week and needs a food change now.
What the 4.0 to 7.0 kg band covers
Queens usually sit at 4.0 to 5.5 kg, neutered males at 5.0 to 7.0 kg, and the extra 1.5 kg is frame and muscle, not fat. A 5.0 kg cat at body condition score (BCS) 5 on the 9-point scale carries roughly 15% body fat; the same frame at 7.0 kg and BCS 7 carries 25% to 30%. Judge with your hands before you trust the scale. Run 2 fingers along the ribcage: you should feel ribs under a thin pad, like the back of your hand, not under a duvet. Stand over the cat: a 1 to 2 cm waist behind the ribs, not a straight tube. A British Shorthair with a broad chest and thick neck reads 0.5 to 1.0 kg heavier than a slimmer breed at the same BCS, which is exactly why the breed range is 3 kg wide.
One weigh-in per month, 3 fixed conditions
Same scale, same time of day, before the first meal. A full stomach and a full bladder move the reading 80 to 150 g, which is 2 to 3 weeks of real change. A baby scale with 10 g resolution costs less than a 2 kg bag of food and beats a bathroom scale, where a 5.0 kg cat and a 5.4 kg cat can show the same number. Log grams in a note: week 1, 4820 g; week 5, 4880 g. Convert to a weekly rate with (new minus old) divided by weeks, and flag anything above 1% of body weight per week for 3 readings in a row — 50 g for a 5 kg cat. Kittens are the exception: from 0 to 6 months they gain 50 to 100 g a week, so weigh weekly, not monthly. If your cat will not sit still, weigh yourself holding the cat, then weigh alone, and subtract; that method carries about 100 g of error, so use it only for the monthly trend, never for a 50 g decision.
The 3 lines and what each one triggers
Line 1 is 4.0 kg. Below it, an adult cat stops any diet and gets a vet visit within 7 days, because loss under 4 kg in this breed usually means muscle, not fat. Line 2 is 5.5 kg: the ceiling for a neutered adult that is not a large-framed male. Cross 5.5 kg and cut the daily portion by 10%, not 30%, then reweigh in 14 days. Line 3 is 7.0 kg. At or above it, switch to weekly weighing and get bloodwork for thyroid, glucose and joint pain before any calorie cut. Most vets cap loss at 0.5% to 1% of body weight per week — 25 to 50 g for a 5 kg cat, or about 1 kg in 4 to 6 months. Faster than that and the cat loses lean mass first.
Weight by age and sex, with daily grams
Use the table as a sanity check, not a target. The last 2 columns assume a dry food at 3,800 kcal per kg and an indoor, neutered adult from 12 months.
| Age | Male kg | Female kg | Dry food g/day | Gain g/week |
|---|---|---|---|---|
| 2 months | 1.0 to 1.5 | 0.9 to 1.3 | 45 to 60 | 100 |
| 4 months | 2.0 to 2.8 | 1.8 to 2.5 | 60 to 75 | 100 |
| 6 months | 3.2 to 4.2 | 2.8 to 3.6 | 65 to 80 | 50 |
| 12 months | 4.5 to 6.0 | 3.6 to 4.6 | 55 to 70 | 0 |
| 7 years | 5.0 to 6.5 | 4.0 to 5.2 | 50 to 65 | 0 |
Calories: 70 times kg to the 0.75
Resting energy need is about 70 x (weight in kg)^0.75. A 5 kg cat needs 70 x 3.34, or 234 kcal, to lie still. A neutered indoor adult multiplies by 1.2 for 280 kcal a day; a cat on a loss plan uses 0.8 x 234, about 187 kcal. A 4 kg bag of dry food at 3,800 kcal per kg holds 15,200 kcal, which is 54 days for the 280 kcal cat and 81 days for the 187 kcal cat. Weigh portions on a kitchen scale in grams. A 240 ml measuring cup of kibble swings 20 to 30 g between brands, and that is 80 to 120 kcal of daily error — enough to add 300 to 400 g a month. Mixing wet food in changes the arithmetic: a 85 g pouch at 80 kcal replaces 21 g of that 3,800 kcal kibble, so a cat on 280 kcal can take 2 pouches (170 kcal) plus 29 g of dry (110 kcal) and stay on target.
When the scale is a symptom, not a diet problem
Book a vet for 5% loss in 4 weeks (250 g on a 5 kg cat), 10% in 3 months, or a gain above 300 g a month after age 7. Loss with a good appetite points to thyroid or diabetes; gain with a poor appetite points to fluid or a mass. Both need bloodwork, not a smaller bowl. Pain also shows on the scale: a cat that stops jumping 50 cm onto the counter and puts on 200 g in 6 weeks is often a cat with sore elbows. Watch the jump height and the 3 jumps per day it used to make, and mention both numbers at the visit.
4 steps for this month
- Day 1: weigh before breakfast, write the grams, and score BCS 1 to 9 with 2 hands on the ribs.
- Day 2: recalculate the daily portion at 70 x kg^0.75 x 1.2, weigh it once, and mark that cup size.
- Day 30: reweigh, divide the change by 4 weeks, and compare with the 1% line (50 g for 5 kg).
- Day 31: if the cat is over 5.5 kg, cut 10% and set a 14-day recheck; if under 4.0 kg, stop cutting and call the vet.
Next reads
The month-by-month routine, including nail and dental slots, sits in the British Shorthair care calendar. For a cat losing weight after 10 years, use the senior weight loss checklist before changing food. If you are still choosing a breed, the breed quiz takes 3 minutes and asks about grooming and space, not looks.
Terms mentioned in this article
Frequently asked
How much should an adult British Shorthair weigh?
Most adults sit between 4.0 and 7.0 kg. Queens usually run 4.0 to 5.5 kg and neutered males 5.0 to 7.0 kg, because the breed carries a broad chest and heavy muscle. Judge body condition with your hands as well, since a 5 kg cat at score 5 and a 5 kg cat at score 7 look very different.
How often should I weigh the cat, and on what scale?
Once a month, on the same scale, at the same time of day, before the first meal. Use a baby scale with 10 g resolution if you can, because a full stomach and bladder shift the reading by 80 to 150 g. Log grams and compare the 4-week trend, not a single weigh-in.
When does weight change mean a vet visit?
Book a visit for a 5% loss in 4 weeks, a 10% loss in 3 months, or a gain above 300 g a month after age 7. Loss with a good appetite points to thyroid or diabetes, and gain with a poor appetite can mean fluid, so both need bloodwork rather than a smaller bowl.