I used this when my boy was a baby and if he was underweight I would increase his food and if he was on the right track I would keep the same amount.
It’s good to have a look at the dogs behind your pup to see how the dogs in his lines turned out full grown if they was compact, slim etc.
I feed raw and used this guide
An adult dog needs around 2 – 3 % of their total body weight each day. To maintain your dog's weight 2.5% and to fatten up a skinny dog 3%. For a porky pooch it is recommended to reduce to 2% to help slim. Puppies may need up to need up to 8 - 10 % of their bodyweight to aid growth.