How do they measure the Metabolic Rate?

There are two primary methods to measuring basal metabolic rate - direct calorimetry and indirect calorimetry. Both of these normally require equipment that most people would not have at their disposal.

Often, a rough estimate can be determined that ranges from 9 to 13 calories per pound .. (9 if you're not very active, 13 if you'r active). And then reducing this by 100 calories for every 10 years older than 30.

The following site gives information about how to calculate the metabolic rate :

http://health.discovery.com/tools/calculators/basa...

http://fig.cox.miami.edu/~lfarmer/BIL265/BIL2001/m...

This explains it pretty well