I like to use this calculator as a guideline:
Metabolic Energy Requirements For Dogs
I know it's a cocker spaniel website, but the calculator is for all dogs, and I have been told by a nutritionist friend of mine that it is fairly accurate for coming up with a guideline to start out with.
I just take the daily kcal requirements the calculator comes up with and use that in conjunction with however many kcals are in each cup of kibble (the bag should say). I never trust the feeding guidelines on the bag, because, them being a dog food company, it's only expected that they'll want you to feed more of their food lol...