For a growing puppy it is probably immeasurable due to a lot of things such as how big he's going to end up, how much energy is he burning everyday. Not every puppy will get the same exercise. That is why the bag that you're feeding will give you a guideline of how much to feed. Look at the kcals/cup and see what the recommendations are and that might give you a ballpark.
I can tell you a dog the size of a Golden or a lab should get between 900-1200 kcals per day based on activity. A working dog in the field 3-5 hours a day could consume as much 2000 kcals a day. Here's a fun fact, Iditarod dogs will consume upwards of 10k kcals a day during the race.
Anyway, trying to figure out how many kcals a day for a puppy is probably a recipe for issues down the road. Just look at the bag you're feeding from and start within 10% of the recommended amounts and adjust as needed. Remember it's always better to keep them lean (not skinny) while the hips are developing as growth plates will close at around 14 months.
FWIW, the pic you attached looks like your dog had plenty of weight on him. Can't tell for sure be he looks like he has a bit more then my girl had while she was 5-6 months old.
Edit...
You also answered your own post sorta. As you said different foods have different kcals per cup. That's why I laugh at people when they say their vet said to just feed 3 cups to a golden or 4 cups without even knowing what they are feeding them. I used to feed a food to my last golden that was 537 kcals per cup and only fed 2 cups a day to (almost 1100 kcals). If I feed 3 cups she's never have a form stool and would have gained weight like crazy. The bag is you starting point and always should be and adjust from there. There is no 1 way to feed all dogs from every type of food.
