1 Kg of our body fat is roughly equal to 7700 calories.ie to reduce 1 kg you need to burn nearly 7700 calories.
So if you burn nearly 1100 calories daily by doing any cardio exercise, in seven days you will be able to burn 7700 calories  ie nearly 1 kg weight loss in a week.
Burn calories and blast fat fast with the best cardio workouts on the treadmill, elliptical, bike or abs procircle.
Its not that easy to reduce 1100 calories daily at a stretch for a  person at the beginning.So its better to split the timings of hitting the gym . Lets say one hour in the morning and one hour in the evening.
One hour in gym you can easily reduce 600 calories by doing any cardio exercise. So doing it morning and evening you can achieve this goal.