It's virtually impossible to figure out how many calories you burn exercising or doing normal activities. Almost everyone overestimates how many calories they burn exercising. See sticky thread:
http://www.3fatchicks.com/forum/exer...g-methods.html.
That's why most people use exercise for fitness, not for weight loss. It's also why people count exercise by measurable goals- minutes exercised, pounds of weight lifted, speed on a 5K, etc.