When you exercise and you feel you are losing weight but to know whether you are losing fat or muscle measuring body fat is essential.
A simple thing I want to share here is, always check your store points in your body where fat generally gets stored first and lose at its end.
For females generally store points are tummy, hips, thigh, and triceps and for average male its tummy.
So tummy is the best part of where you can check whether you are losing fat or muscle which tells you whether your nutrition and workout is proper or you are going on the wrong track.
The best method is, Pinch your skin ie 4 fingers from your naval line and check the thickness before you start your workout regime, and check again after 15 20 days.
You are losing weight and if the thickness of the skin is the same then something is wrong, which means you are losing muscle not fat.
If u lose skin thickness and even if u do not lose weight that means you are on right track and losing fat.
This is the simplest and easiest way of measuring whether you are losing fat or muscle.