A kilocalorie or food calorie is a unit of energy used to measure the chemical energy in food. It is generally defined as the quantity of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. You can estimate the caloric value of food from the amount of carbohydrates, fats, protein and dietary fiber that it contains. This value will be an estimate because the efficiency with which food is digested varies considerably.
Read the nutritional label. Obtain the number of grams of fat, total carbohydrates, dietary fiber and protein in a serving of the food. You will also need to obtain the serving size of the food.
Calculate the calories provided by fat. A gram of fat contains 9 calories so multiply the number of grams of fat by "9" to get the number of calories in a serving that come from fat.
Determine the calories provided by protein. A gram of protein contains 4 calories so multiply the number of grams of protein by "4" to get the number of calories in a serving that come from protein.
Establish the number of calories that come from non-fiber carbohydrates. Non-fiber carbohydrates have about 4 calories per gram. Subtract the number of grams of dietary fiber from the total grams of carbohydrates. Multiply this value by "4" to get the non-fiber carbohydrate calories.
Compute the number of calories from dietary fiber. The digestibility of fiber may run the range from completely indigestible to almost completely digestible. Use the middle of this range (2 calories per gram) to estimate the calories from dietary fiber. Multiply the number of grams of dietary fiber by "2" to obtain the approximate number of calories that come from dietary fiber.
Find the total number of calories that come from the serving of food. Add the calorie counts from Step 2 through Step 5 to find the total calories in the food.