There's a RMR test called the BodyGem that's offered by Ballys and other gyms. The test here runs about $50 and you don't have to be a member to get it. It takes about ten minutes and measures oxygen usage (O2 is the fuel of metabolism). You clip a nose plug on your nose and breath through this device:
You take the RMR number that the device gives you and multiply it times a formula based on your activity level to come up with total calories burned in a day. The RMR number is supposed to be pretty accurate, but the activity multiplier is just an average, of course, so subject to error.
I've given at least 100 BodyGem tests to women and gotten RMR read-outs between 965 calories (a tiny 72 year old woman) up to over 2600 calories (a young, very obese woman). It's interesting to figure out where you fall in that spectrum!
I've done the test twice myself ... the first time was right after I had finished losing weight and my RMR was 1365. After a year of maintenance and weight lifting, it increased to 1600. Yay muscle!!
If anyone is interested in a RMR test, try calling the gyms in your area to see if they offer it.