Multiply your dog's healthy body weight by .02 to .04 to get the estimated feeding amounts in pounds-per-day. Preferably, divide this into two daily feedings; breakfast and dinner. (For example, a 5 yr old, 50lb dog that get's a couple of short walks per day would most likely fall in the middle of this range so .03 * 50 = 1.5lbs of food per day or .75lbs per feeding, twice daily).
This is only a guideline and can vary based on your dog's age, health and activity levels. Pregnant or lactating dogs and puppies can eat twice
this much. You'll want to monitor your dog's weight for the first few weeks to determine the correct amount for them.