Is there a test that determines a person's exact basal metabolic rate?

Answer 1

Basal metabolic rate can be estimated through a number of formulas. Exact measurement involves a piece of special equipment called a room calorimeter, which to the best of my knowledge measures very slight changes in a temperature controlled room to estimate how much energy you're expending based on the amount of heat you're putting out.

Answer 2

Here's an article explaining it. Essentially it's the caloric measurement used to maintain your current weight. In theory and practice, reducing your intake below your BMR will help you lose weight.

http://www.ehow.com/how_5401507_lose-off-using-simple-math.html