The difference between a calorie and a kilojoule is primarily a matter of measurement. A calorie is a unit of energy defined as the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius. A kilojoule is a larger unit, equal to 239 calories. In nutritional contexts, understanding these measurements helps individuals track their energy intake and manage weight effectively. Both units are crucial for dietary guidelines and understanding energy balance in the body.