The number of calories you need to breathe--or to just exist without expending any additional energy--is your resting metabolic rate. Your physical condition, age and gender all affect your RMR.
Calculation Method
To find out how many calories you need to breathe, multiply 0.02 by your body weight in kilograms. Then multiply the result by the amount of time during which you want to know how many calories you burned.
Result
One kilogram equals 2.2 lbs. of body weight. So if you weigh 150 pounds, multiply 0.02 times 68 kg. The result is approximately 1.4. Multiply 1.4 times 15. You burned 21 calories breathing for 15 minutes.
Variables
If you are physically fit, you will require slightly more calories to maintain your RMR than if you are out of shape. The Marquette General Health System indicates that muscles use approximately 75 percent of the calories you need at rest. Your RMR is higher in early adulthood and women need between 5 percent and 10 percent fewer calories than men.
