The generally accepted data is that there are 3500 calories in 1 pound of body fat.
So if you wanted to lose weight at a rate of 1 pound per week, you would need to reduce your overall calorie intake by 3500 calories, or 500 calories per day.
Check out the YouTube video above which explains how you can lose weight by just reducing your calorie intake and creating a calorie deficit (more calories spent than calories consumed.