According to the Mayo Clinic, 3,500 calories are equal to about 1 pound. Because calories are a unit of heat and pounds are a unit of weight, there is no direct conversion, and calories per pound differ with each person.
A person's metabolic rate determines the amount of calories that are equal to a pound, the Mayo Clinic details. The metabolic rate affects the number of calories and the speed at which they burn. The functioning of a metabolism varies based upon a person's size, sex, age, genetics and daily physical activity. According to WebMD, those who consume more calories also have a faster metabolic rate, requiring more than 3,500 calories to gain 1 pound.