How many calories do you burn? I walk for 30 minutes every day. Is there an easy formula to figure how many total calories I'm burning?

Shape, Sept, 2004 by Suzanne Schlosberg

Q I'm 5-foot-5,35 years old, weigh 145 pounds and walk half an hour daily. What is the formula for determining how many calories I burn a day?

A To get a relatively accurate number, says Jackie Berning, Ph.D., R.D., an associate professor of nutrition at the University of Colorado at Colorado Springs, try this simple step-by-step formula for women:

1. Calculate your weight in kilograms by dividing your weight in pounds by 2.2. You weigh 65.9 kilograms.

2. Multiply this number by 0.9. This is your average hourly calorie burn. Yours is 59.31.

3. Multiply this number by 24 and you get your approximate BMR (basal metabolic rate, aka RMR, or resting metabolic rate), the number of calories your body burns simply to stay alive--to keep your heart beating, your lungs expanding, your liver functioning and so on. Yours is approximately 1,423 calories.

4. Calculate your activity level:

* If you live a basically sedentary life, add in 10-20 percent of that number and you'll have your daily calorie burn: 1,423 213 (15 percent of 1,423) = 1,636.

* If you do light activity--you have, say, a desk job--but you walk 30 minutes a day--add 50 percent of your BMR; for you, this would be 2,135 calories.

* If you have a moderately active job--for example, you're a teacher and on your feet much of the day and you do a vigorous daily workout for at least 30 minutes, add 70 percent. This would equal 2,419 calories.

* If you have a very active job, such as a mail carrier, and do daily vigorous workouts for about an hour, add 80 percent--which comes to 2,561 calories.

So, based on your specific activity level, you are burning about 2,135 calories per day.

Another formula to calculate your approximate BMR is the Harris-Benedict. For women, it is: 655 (4.3 X weight in pounds) (4.7 X height in inches) - (4.7 X age in years). By this formula, your BMR would be 1,420 calories--pretty close to the calculation above.

Of course, both formulas only give you an estimate. To more precisely gauge your BMR, you will need to visit a gym or hospital equipped with machines that measure your caloric consumption through your respiration. The BodyGem, for example, requires you to breathe through your mouth into a tube for five to 10 minutes. The machine then analyzes the composition of the gases in your breath to give a pretty accurate BMR, provided you haven't exercised or eaten recently.

Send your questions to Shape, Weight-Loss Q & A, 21100 Erwin St., Woodland Hills, CA 91367; fax: (818) 704-7620; e-mail: WeightLossQ&A@Shape.com.

Suzanne Schlosberg is the author of The Curse of the Singles Table: A True Story of 1001 Nights Without Sex (Warner Books, 2004).