The average daily intake of food among Australian adults is 8,700 kilojoules a day, according to SA Health. The exact amount a person should eat depends on his age, sex, weight and activity level. Kilojoule is the metric equivalent of calorie.
A person needs to take in about 120 to 140 kilojoules per kilogram of body weight per day, suggests Reader's Digest Australia. To maintain his weight, a person weighing 68 kilograms needs to eat 8,100 kilojoules a day if he is sedentary, 8,850 kilojoules a day if he is slightly active and 9,500 kilojoules a day if he is active. The Australian Government Department of Health provides a chart of kilojoules per day for males and females at different age groups. The department offers an online nutrient calculator for estimating the kilojoules from food and drinks that a person should consume in a day.