It depends on the shop, the cut, your body shape, posture and fitness etc etc.
I am exactly the same weight now as I was last month, but have not been able to exercise for a few weeks (circuit/interval training). As a result, the clothes that were falling off me last month are now a bit snug and in the case of one particular pair of jeans, positively uncomfortable.
After about a week of working out daily I tend to find that my clothes start to fit properly again.
A year ago I weighed just under 15 stone and was a size 18 squishing myself into size 16 clothes. 
Today I am 5' 7" and currently weigh 10 stone 13 lbs and am, mostly, wearing a size 12, with a couple of my old 14s thrown in for comfort. I can't go smaller than a 12 etc in jeans etc, even though the waist is always baggy, because I now have muscley (sp?) legs.
Next week, without a doubt and with no dieting, I will weigh 10 stone 11lbs (currenly have PMT
) but it will have very little affect on the fit of my clothes. For me its good quality high intensity exercise that makes the difference.