How much is the Nutritional requirement of human in calories?

The amount of calories required per day varies from person to person, however there are guidelines for calorie requirements you can use as a starting point.

The UK Department of Health Estimated Average Requirements (EAR) are a daily calorie intake of 1940 calories per day for women and 2550 for men.

However the amount calories that are needed each day can vary greatly depending on lifestyle and other factors.
That depends on your activity level. If you're a couch potato, 1200 to 2000, if you're a football player in spring training, as much as you can eat.
The Harris Benedict equation is a good tool to determine average daily calorie expenditure; however, it is a mathematical equation and not perfect.