In my experience, these kinda of things are very difficult to calculate as it depends very much on you as an individual -- not just your weight, but you physical makeup, your pace, your incline, etc. etc.
I wouldn't worry about getting an exact number -- you're getting a great workout, so yay for you! I almost never eat back any exercise calories burned, so to me it doesn't really matter what those numbers are.
Loving yourself is an act of will. It doesn't just happen, you have to choose it.
My blog: Bliss-a-go-go!
: I'm generally inappropriate and I over-share.)