It depends on how much you weigh. The less you weigh, the less weight you have to lose before you get to the next size. For example I am a size 26 (but have to wear a belt so not even) and STILL I know i can't wear a 24 until I lose 30 lbs. To get to a 22 after that I have to lose another 30...then 20 to get to a size 20...etc.
for every TEN: