I'm pretty sure everyone who cares about getting a good fit (and isn't simply trying the clothes on in person) is looking at measurements, which you can usually find for any half-decent vendor (though it may take some poking around their site). The best have it per-garment (or per-cut), less-good but usually still alright is having a guide to the measurements they base their sizing off of.

Even guys can't really get away with just "Small, Medium, Large" if they want a decent fit that they can predict from just the label. Modifiers for the cut become necessary (regular, slim, relaxed, extra-slim, that kind of thing). And that's for clothes that are pretty forgiving on the fit, like knits...

Women's clothes are even trickier. It's basically impossible to boil them down to one or even two size metrics or labels unless you're relying on a shitload of stretch in every other part of the garment, which is something that usually only very bad garments do (think: Temu). Women's proportions are also far more variable. Shoulder-bust-waist-hip often sees some pretty wild differences, like two women will match on a couple of those measurements and be way far apart on the others. Then you've got height to worry about. Dudes can be similarly far outside the norm of distributions for the relations between their key measurements, but it's not as common—most of us have it relatively easy.

Looking at the actual measurements, though, I've found to be very reliable. I buy almost all my clothes on eBay and directly from brands on their websites, with great success, because I know both my own key measurements, and the dimensions of clothes that fit me well (I have some notes, doesn't take a lot of data points to have enough to be pretty accurate). I've also ordered for my wife with a similar strategy, works well there, though you're way more likely to run into cases of "OK there are zero sizes of this garment that will work for you, just gotta give up on this one" because of the issue above.

Ironically, one area that both genders can have trouble with is crotch seam length, though typically on opposite sides of the garment — but in women’s clothing it’s often worse than men’s due to the spectrum of “extra high rise” to “extra low rise” that’s added to the mix in women’s clothing. Aligning with the hourglass-mostly point of the article, the most common is High Rise, which corresponds to the higher ‘resting point’ on the torso cylinder for a waistband when women have gained fat deposits in the usual rearward hourglass places (as otherwise the waistband sits at a severely sloped angle from back to front). For rectangle or triangle folks, you will rarely find Low Rise or Extra Low Rise that have the appropriately-shortened crotch seam. For spoon folks, you have to shop at shops that cater to spoon shape, because most major retailers only cater to one specific shape and stretch simply isn’t enough to compensate for the rectangular to spoon difference (as Lululemon discovered a decade ago or so). That’s because two women with upper leg circumference 30 may have hip sizes varying from 20 to 60, depending on which body type they have and where their fat deposits are — and the two ends of that spectrum do not indicate anorexia/obesity, either. Body shape and fat levels vary that widely under normal healthy circumstances. I envy men’s jeans for their (relative, but not zero) simplicity.

eBay? Can you elaborate? Do you mean used clothes like on Poshmark? And does eBay really publish decent clothes measurements?

> Women's clothes are even trickier

Oh that explains why my wife spends so much time obsessing over clothes: trying clothes, buying/returning, buying others, etc. I'm sure a few others can relate.

And she's got a very normal BMI: not underweight, just plain in the middle (5'5" / 124 lbs: something like that) and a very hour-glassy/feminine shape, so many clothes are "made" to her shape/size/weight. I can't imagine what it'd be if she had uncommon "dimensions".