Today, I learned one of the basic equations dieticians use to help determine how many calories a person needs. While there are other, possibly more accurate methods to come up with the appropriate number, this is great for giving you a general idea.
You multiply body weight in kilograms (1 kg = 2.2 lb) by 25-30 calories, depending upon the level of activity.
a 140-lb person weighs about 64 kg ( because 140/2.2=64)
If this person is very sedentary, they can calculate their caloric needs by multiplying 64 by 25.
64 x 25 = 1,600 calories/day
If they are very active, they multiply 64 by 30.
64 x 30 = 1,920
If the person is moderately active, they can find out the average of these numbers to determine how many calories they require a day.