How much should I feed a 18kg dog?

Resting energy for an 18kg dog is around 612 kcal, and a typical neutered pet at normal activity needs roughly 1.6 times that, close to 980 kcal a day. At 350 to 400 kcal per 100g, that comes to about 250 to 270g of dry food.

This is the figure for a dog getting regular walks and some off lead time, not a dog working all day.

A genuinely working sheepdog or a dog doing several hours of structured, high output activity a day can need two to three times resting energy, sometimes 1,200 to 1,800 kcal, which is roughly 320 to 480g of a standard dry food or a switch to a higher calorie working formula.

Do not apply a working dog's amount to a pet dog of the same breed and weight, since the difference in output is large enough to cause steady weight gain.

If your 18kg dog is gaining weight on the standard pet amount, first check whether daily activity has genuinely dropped, since border collie type breeds often look thin even at a healthy weight due to their build.

Feel the ribs rather than relying on appearance alone, since a lean looking dog can still be carrying more fat than it seems. A photo taken from directly above at the same time each month can make a subtle shift easier to notice.