Clothing sizes do have many variables. The clothing industry basically abandoned the standard cloth-sizing agreement in the 1980s. What used to be for instance, a size 10 became a size 4, size 14 became an 8, size 18 became a 14 and so on.
How much weight you lose to drop a dress size however depends on how big you are to start with. It’s probably easier to understand if we start from the smallest size. Imagine a stick-thin model putting on a few pounds, she would probably shoot up one or maybe even two dress sizes through only gaining, say 3 or 4 inches around the waist and bust combined. At the other end of the scale dress size could be hardly affected at all even with a loss of 20 or 30 lbs, that’s for someone over 250 to 300 lbs of course.
If we look at the official figures on the old standard, dropping from a size 12 to a 10 which is a modern 6 to a 4 would have meant a combined loss of 3 inches in total from the bust, waist and hips equating to a loss of 10 lbs. Remember back then of course it was considered that shorter people were going to be generally smaller. I think that was based on the average woman’s height at the time being 5’4″.
At the other end of the scale someone who was a size 50 would have according to the clothing manufacturer’s standard of the day, being around 5’6″ and in order to drop 2 dress sizes, they would have lost 15 lbs and 6 inches around the bust, waist and hips combined.
The thing is as much as for the ladies and the men, those sizes have changed so much over the last 30 or so years that they don’t mean a lot at all anymore. I shop between four different countries, the sizes the manufacturers chose relate very much to the demographics of the population they serve. For instance a large T shirt bought in the UK would be an XL T shirt for the same size in France and an XXL for the same size bought in Italy.
So the bottom line is really, it’s not what size clothes we’re buying that matter so much, its how looser the clothes that we bought last time that’s what gives us the thrill.