Here's a Harris Benedict Formula example of how to determine the amount of calories (BMR rate) you burn while resting.
WARNING: Use this equation only as an estimate.
Example 1
Susan is 45 years old; she weighs 245 pounds and is 5 foot 5 inches tall. She works a job where she sits most of the day. She never exercises. Based on these statistics, how many calories is Susan daily?
Step 1
Plug Susan's weight (245lbs), height (5 foot 5 inches), and age (45 yrs) into the formula below for women to find her BMR.
English BMR Formula 
Women: BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches)  (4.7 x age in years)

BMR=655 + (4.35 x weight in pounds) + (4.7 x height in inches)  (4.7 x age in years).
BMR=655 + (4.35 x 245) + (4.7 x 65)  (4.7 x 45)
BMR=655 + 1065.75 + 305.5  211.5
BMR= 1814.75
Step 2
Determine Susan's activity level using the chart below
Harris Benedict Formula 
To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:
* If you are sedentary (little or no exercise): CalorieCalculation = BMR x 1.2
* If you are lightly active (light exercise/sports 13 days/week): CalorieCalculation = BMR x 1.375
* If you are moderately active (moderate exercise/sports 35 days/week): CalorieCalculation = BMR x 1.55
* If you are very active (hard exercise/sports 67 days a week): CalorieCalculation = BMR x 1.725
* If you are extra active (very hard exercise/sports & physical job or 2x training): CalorieCalculation = BMR x 1.9

Step 3
Plug numbers into the formula
Since Susan doesn't exercise and inactive she is sedentary according the chart above. Based on that information, multiply her BMR X 1.2
Plug in the appropriate numbers
Susan's calories burned while at rest = SUSAN'S BMR X 1.2
Susan's calories burned while at rest = 1814.75 x 1.2 = 2177.7
Susan burns approximately 2177.7 calories a day at rest
Download Medium size (17" by 11") Harris Benedict formula chart.