A cat that gains 300 g in a year on a diet you never changed has one likely culprit: the scoop. A 240 ml measuring cup holds anywhere from 60 to 110 g of dry food depending on kibble size, shape and how the cup is filled, so the same scoop can put 20 to 40 percent more calories in the bowl than the portion you planned. A kitchen scale that reads to 1 g costs 15 to 30 USD and removes most of that error inside a week.
A level cup is already 37 percent over
Start with the cup itself, before anyone heaps it. Dry food sits at 0.30 to 0.45 g per ml, so a level 240 ml cup weighs 72 to 108 g. A 4.5 kg neutered adult cat needs about 240 kcal a day, which is 63 g of a 3.8 kcal/g kibble. The level cup weighs 86 g. That is 23 g and 87 kcal extra every day, 31,900 kcal a year, and about 4.1 kg of body fat at 7,700 kcal per kg. Nobody in that house thinks the cat is overfed, because the label was read correctly and the cup was level.
Heaping, shaking and switching brands
The 20 to 40 percent spread lives in the parts owners do not measure. A heaped cup adds 15 to 25 percent over level. Shaking the cup so the kibble settles adds 10 to 15 percent. Moving from a small ring-shaped kibble to a large flat one changes the same cup by 25 to 40 percent, because the pieces pack differently. Stack a heaped, shaken cup of dense kibble at 0.45 g per ml and you reach 130 g where the label calls for 60 g. That is also how 2 cats on one food end up at 4.5 kg and 6.8 kg, and why grams are the only unit that survives a brand change.
What 1 g resolution buys you
On a 60 g ration, 1 g is 1.7 percent and 5 g is 8.3 percent. A 5 g postal scale is workable, 1 g is better, and a 0.1 kg bathroom scale is useless because its 100 g step is bigger than the item. Pet and baby scales in the 20 to 40 USD range read to 1 g, hold a tare and run 6 to 12 months on 2 AAA batteries. Check yours monthly against a 100 g reference weight or a sealed 500 g bag of rice; if it drifts more than 2 g, replace it. Tare the bowl every time, since a ceramic bowl weighs around 380 g and 2 meals a day give you 2 chances to forget.
Weigh 3 times a week
On 3 mornings a week, Monday, Wednesday and Friday, weigh the day's dry ration into a sealed container and feed only from it. Three points a week catch a new bag, a new scoop or a helpful family member within 48 hours; one point a week catches the same change after the cat has eaten 6 extra meals. Keep the scale on the counter rather than in a drawer, because a scale 2 steps away gets used 5 times a week and one inside a cupboard gets used twice a month. Weigh the cat every 14 days on 5 g resolution and log both numbers in the same place.
The 500 to 900 kcal you cannot see
Precision still matters after the cup is gone. A systematic bias of 0.6 to 1.1 percent on a 60 g ration is 0.4 to 0.7 g a day, which is 1.4 to 2.5 kcal a day, which annualizes to 500 to 900 kcal and 65 to 117 g of fat. That is roughly the error a 4.5 kg cat absorbs without changing weight, so it is also the margin you are trying to hold. The cup error is 30 to 60 times larger: a 20 to 40 percent overscoop is 12 to 24 g of kibble, 46 to 91 kcal a day, 16,800 to 33,200 kcal a year and 2.2 to 4.3 kg of fat. Same cat, same bag, two very different outcomes.
Do the gram math once
Multiply body weight in kg by 70 and raise it to the power 0.7 for resting energy, then use 1.2 for a neutered adult, 1.0 for a weight-loss plan and 1.4 for an intact active cat. Divide by the calorie density printed on the bag, usually 3.8 to 4.2 kcal/g for dry food. The table does it for 5 weights, with a level 240 ml cup at 86 g for comparison. A 6.0 kg cat eating 100 g from a plus-30 percent scoop takes in 380 kcal where 294 is the target.
| Body weight | kcal/day | g at 3.8 kcal/g | g at 4.2 kcal/g | g in a level 240 ml cup | g eaten at +30% |
|---|---|---|---|---|---|
| 3.2 kg | 190 | 50 | 45 | 86 | 65 |
| 4.0 kg | 222 | 58 | 53 | 86 | 75 |
| 4.5 kg | 241 | 63 | 57 | 86 | 82 |
| 5.2 kg | 266 | 70 | 63 | 86 | 91 |
| 6.0 kg | 294 | 77 | 70 | 86 | 100 |
Wet food changes the arithmetic
Wet food runs 0.9 to 1.1 kcal/g at 75 to 82 percent water, so an 85 g can is only 80 to 90 kcal and looks like a big meal for very little energy. A 4.5 kg cat eating half its calories wet takes about 120 kcal from wet food, near 125 g or 1.5 cans, plus 32 g of dry. That split has to be set in kcal, not in spoons, which is the whole argument in the wet food ratio guide; the calorie and water differences behind it are in wet versus dry food.
Treats and human food, by weight
Treats are where the arithmetic quietly breaks. One 3 g freeze-dried treat is 11 to 12 kcal, which is 5 percent of a 4.5 kg cat's day, and 6 of them is a 30 percent overshoot. Hold treats to 10 percent of daily calories, about 24 kcal here, and weigh them on the same scale. Human food is worse than a calorie problem: onion, garlic, grapes, xylitol and alcohol are all on the no list at doses far below a spoonful, so check the toxic food list before you share a plate.
Five steps for this week
- Buy a 1 g scale, tare a bowl and write the gram target for your cat's weight on the lid of the food container.
- Weigh food on Monday, Wednesday and Friday; keep the scoop in a drawer and use it only for the last 2 g.
- Weigh the cat every 14 days and change the gram target after any 200 g move in either direction.
- Recalculate whenever the bag changes, since 3.8 versus 4.2 kcal/g is an 11 percent swing on the same grams.
- Keep treats under 24 kcal a day and count them in the same log as the meals.
Frequently asked
Is a 5 g postal scale good enough instead of 1 g?
It is workable but leaves visible room for error. On a 60 g daily ration, 5 g is 8.3 percent, which annualizes to roughly 5,000 kcal and about 650 g of body fat, so the scale you already own can still hide half the problem. A 20 to 40 USD pet scale reads 1 g, holds a tare and pays for itself the first time it stops a 300 g weight gain.
Do I still need to weigh food if I use wet food only?
Yes, and the numbers are smaller so the errors are easier to miss. An 85 g can is 80 to 90 kcal, so a 20 percent overscoop of half a can is only 8 to 9 kcal, but that is still 3,000 kcal a year. Weigh cans in grams, split by kcal rather than by spoons, and check the water and calorie differences between formats before switching.
How do I know the gram target is right for my cat?
Use 70 times body weight in kg to the power 0.7, then multiply by 1.2 for a neutered adult, and divide by the kcal/g on the bag. Feed that number for 14 days, weigh the cat on 5 g resolution, and adjust by 5 percent if the weight moved more than 200 g in either direction. A 4.5 kg cat lands near 240 kcal and 63 g of a 3.8 kcal/g food.