3,500 calories burnt is one pound lost. Karin brought up a great point when she said that exercise equipment offers an approximation at best as far as accurate caloric expenditure goes. To figure out exactly what your metabolic rate is at any given time, you have to look at METs. As a measure of oxygen uptake in ml/kg/min… 1 MET is about 3.5 ml/kg/min… What’s cool about METs is that some pieces of equipment that measure METs (by estimate) can help trainers to figure out what the intensity of the exercise is for the client. Really heavy intensity exercise like jumping rope is about 10 METs. This translates into a kind of RPE chart without the chart, roughly.
Of course, Resting Metabolic Rate is dependent upon so many different extraneous environmental and physical factors, that even MET measurements are, unfortunately, a best educated guess unless in a medical setting with proper equipment to measure everything and control for other stuff.