Are there any accurate activity/calories burned calculators?

I went to 5 different websites to try to get an idea of how many calories someone at my age, weight and height would burn by walking 2 miles. I've gotten answers ranging from 150 to 225 calories, that's a big difference! I'd really love to have a clue of how to find out how many calories I burn during an activity, I just don't know which site to go by, any suggestions?

If you want to be truly accurate, your best bet is a heart rate monitor.  It calculates calories burned using your heart rate.  A good rough estimate, though, is 100 calories/mile for a 150# person.   I don't count calories at all (eaten or burned), but I know other people at my gym use heart rate monitors all the time.  It is also helpful for training goals.  Linn

The one that I like and makes the most sence to me is that someone burns 70% of their body weight in calories for every mile.   I like it because it takes into account intensity and duration.  If you run or walk hard you will burn more but you wont be out there for long.  If you walk leisurely you won't burn as fast but you will be out there burning longer. At 250 lbs, I burn about 170 calories per mile wether I run fast or slow.