I assume what you're talking about is
Basal Metabolic Rate. You could use one of the many calculators available online which would give you an estimate based on the population you're most similar to but would fail to tell you anything about you specifically relative to that population.
My understanding of the method to find your own is that involves fasting and then measuring your oxygen consumption while resting. This is rather laborious thing to have done just to satisfy your curiosity. Is there a particular reason you wanted to know?
Also, I don't think there is any hard rule to say that you have a fast metabolism at X calories per hour. My best guess would be that at 1 standard deviation or more above the mean for your demographic it would be safe to say that you have a fast metabolism, but really, I just made that up and most people aren't going to understand what you mean by it.