Don't worry its quite normal for the waist to be different brand to brand, its not you shrinking and expanding

If you are a 33 waist then a size 32 RMC/Yoropiko will fit like normal jeans, and a size 34 will be slacker but not saggy, so I would go for the 34 waist. When you first wear RMC they will feel tighter round the waist than after you have worn them a couple of times, so don't panic if when you first get them they are not as loose as you had hoped. Also consider only Dry Cleaning them so you dont get any shrinkage, once you have the size you want, you dont want them to no longer fit you! Best of luck buddy
