Yeah, you are not supposed to wash your STF 501s. However, eventually, they need a bath.
When it comes to washing 501s, this means getting them wet or soaking them and then allowing them to dry. It doesn't necessarily mean putting them in the washing machine. Of course, if you put them in a dryer they will shrink significantly. However, even if you do the Levi's recommended bathtub soak and line dry, you will see shrinkage. I say this from experience with two pairs (i.e., I spent an extra $100 so that you don't have to!)
The thing is, unlike other Levi's that have 1 or 2% elastane, these have minimal to no stretch. So once they shrink in the waist, its like wearing a tight cotton cord around your waist. The trick is that you can't necessarily judge by your Levi's with elastane, or other fit numbers, to be completely sure about the waist.
For me this meant 2" up in length (with no cuff) and 2" up in waist--and this with only a tub wash and line dry.
PS. Why buy STF 501 at all? The fabric is completely different than your other Levis. It is much heavier, like canvas. It also has a different texture, and even smells different. The other reason is you really like your Levis.
"If you plan to wash these jeans, order a larger size. For your waist, increase 1” for sizes 27-36”, 2” for 38-48”, and 3” for 50” and up. And for your inseam, increase 3” for 27-34” and 4” for 36” and up."
I'm not sure why Amazon doesn't put that in the product description. It seems pretty crucial. I hope they update it.
For me, I want jeans that can actually hold up to doing some physical labor in. These fit the bill. Also, faded, worn-in jeans just look better when you wear them in yourself. Sure, they're a little stiff at first, but they loosen up nicely over time and they are tough as hell. Also, I think the "never wash your 501s" rule is silly. Wear them until they are gross. A little gamey is fine. That's how you know you're doing it right. Then wash them. They will be too tight the first time you put them on after washing, but after a few hours they will be right back to their proper fit. This is probably true with all jeans that don't have lycra in the denim, and what business does lycra have in jeans anyway?