Without knowing your heart rate, body fat percentage (since muscle burns more calories than fat), and the temperature while you are exercising, I just don't see how any of those calculators can be close to accurate. I agree with Baffled about not eating more to make up for calories burned though exercise. I take all of their calculations with a very big grain of salt!
I use the calculators on the machines as a way of comparing how I do from day to day. For example, if yesterday the elliptical told me I burned 100 calories and today I get on the very same machine and it tells me I burned 150 calories, I know I worked a little harder today. That's particularly useful on the elliptical, where I have to set the pace myself.
FYI, I checked a couple of other sites:
- CaloriesPerHour.com said 286 calories for a 166-lb person walking at 3.5 miles/hour for one hour.
- HealthStatus.com said 326 calories for one hour at only 3 mph pace (didn't have the option of 3.5 mph).
- The Bally Fitness website said 286 calories for a 3.5 mph pace.