It is confusing because there are 2 types of calorie - the "small" or "gram" calorie which is only ever really used in scientific measurements, and the "large" or "kilocalorie" (Kcal), which is the calorie that we are familiar with from nutrition information, diets etc.
One kilocalorie is the energy required to increase the temperature of 1 kilogram of water by 1°C, and is exactly 1000 "small" calories.