Google calorie needs calulator, or on the good housekeeping website you can find a formula to use.
if you go to Mayo clinic online they have a calorie calculator. you can put in you height weight and level of daily activity, plus weither your looking to gain, lose, or maintain your current weight. And it will calculate how much calories you need to take in per day here is the link:
http://www.mayoclinic.com/health/calorie-calculator/NU00598
It depends upon your weight, how you spend your day (walking, sitting, running etc.) and your basal metabolism, which vary with age and genetics.