How much should I feed a 40kg dog?

Resting energy for a 40kg dog is around 1,114 kcal, and a typical neutered adult at normal activity needs roughly 1.6 times that, about 1,780 kcal a day. At 350 to 400 kcal per 100g of dry food, that comes to about 465 to 490g.

Notice that this is not double the amount for a 20kg dog, even though the weight is double, because larger dogs need less energy per kilogram than smaller ones.

A common mistake is assuming a dog twice the weight needs exactly twice the food, which consistently overestimates the true need for large breeds and can lead to slow weight gain over months.

The safest approach is to calculate fresh from your dog's actual weight using the resting energy formula rather than scaling another dog's portion by eye.

Large breeds can carry a modest weight gain without it being obvious, since a couple of extra kilograms spreads across a bigger frame. Monthly weigh ins on a reliable scale help catch this early.

Feel along the ribs and check the waist from above every few weeks, and adjust the total by about 10 percent if the trend runs upward for more than a month. A written log comparing weight over several months is far more useful for spotting a slow trend than comparing readings taken only weeks apart.