So much this for consistency. I remember one particular bad occasion I went shopping for trousers in a store. I tried five, each had something wrong in relation with the size numbers.

First didn’t fit because it was too tight, so I tried one size larger. This one was even smaller than the previous one. So I tried an even bigger one which was only taller. Tried a bigger number now it was way too big. So for fun I tried one with a higher number which turned out to be smaller than the previous one.

When I asked the store assistant, they shrugged and said that was just reality and why you need to try every item individually. It has to do with how much “spare” cloth the seamstress takes when stitching the trousers together, if the original piece of cloth was even already cut to size properly.

These days I buy from the brand own size, the same item and it fits every time.

I’ve only seen that issue in extremely cheap, China-made, clothing.

It helps to buy high quality, and expensive, clothing. Sizing is consistent, and shape stays after multiple washes.

Googling BIFL in Reddit helps a lot.