1. Know Your Measurements
Take the half-hour or so you need to grab ameasurement guide and get your measurements written down — all of them, not just the waist and inseam.
If you know what you need in your seat, crotch, and thigh as well as your waist and inseam, you can quickly test any pair of pants with a flexible tape measure (less than $10 at any crafts store, and easy to stick in a pocket). Save your measurements on your phone, or on a slip of paper in your wallet, or just mark them on your tape measure itself, so that you’ve always got them with you when you go clothes shopping.
That’ll let you quickly triage most clothes out of the way without ever bothering with the changing room. It helps with online shopping too — more and more brands are starting to list specific measurements beyond the basic waist/inseam pairing for their online sales, to reduce the amount of returns they have to process.
The nice thing about using your body’s measurements is that they don’t change much. Vanity sizing may make clothes harder to judge, but once you know the length of your seat or your crotch, that’s not likely to change much. An inch or two with noticeable weight gain is about all the variation you’re going to see.
2. Measure Your Best-Fitted Clothing
Everyone’s got at least one piece of clothing that’s an old favorite with a perfect fit. If you’re lucky, you’ll have both a pair of pants and a shirt that fit the bill (no pun intended).
Check the measurements on those garments, both the ones on the tag and the actual, physical measurements as taken with a tape measure.
Make sure you know the waist, inseam, crotch, and thigh measurements of your favorite pair of pants, and the collar, sleeve, and chest measurements of your favorite shirt. If you’re shopping for things that are at least in the same neighborhood as those measurements, you’re much more likely to get a fit you like.