Despite the precise-looking displays on machines at gyms and the official-looking published charts of exercise and calories, it’s actually all but impossible to accurately estimate of the number of calories you burn.
Your heart rate is a good gauge of your efforts, but heart rate does not translate easily into calories. Two individuals of the same age, gender, height, weight and even the same level of fitness can burn a different amounts of calories while exercising. If the average number of calories burned with an exercise is 100, individuals can burn anywhere from 70 to 130 calories.
The displays on cardio machines are almost never accurate, with the possible exception of treadmills. But even treadmills are inaccurate if you hang on the rails, which reduces the number of calories burned by 40 to 50 percent.