Inches are actually a good indicator of how well your fitness program is progressing in comparison to weight. Now when we can lose weight by losing the water, muscles as well as fat. But the goal should be to lose fat and gain lean muscles. But because lean muscles are denser than fat, it is also heavier. So if you gain muscles you gain weight as well.
Now fat also takes up 4 times as much space compared to lean muscle. So when you lose fat and gain weight even if your weighing machine shows the same weight, you would still lose some inches. So if you are losing inches but not weight, you don't have to worry since you fitness program is still on the correct track.