At my gym, I paid $40 last year for a Resting Metabolic Rate test- showed up in the morning without having eaten, exercised, or expended any sort of serious energy. I clipped my nose off and breather into a device hooked up to a PC that measures oxygen burn rate and whatever else it captures. After a 10-15 minute seated and resting baseline period, the actual test took another 10-15 minutes.

Anyway, long story short, it came up with 1,410 calories/day, doing nothing but living and breathing. I'm 5'8", 165lbs, and 31 at the time (and before I had any muscle on me at all). Online calculators put me in the 1,500-1,600/day range.