How do I size raw or shrink-to-fit denim?

It depends on one spec: sanforized or not. Sanforized raw denim is pre-shrunk, so you buy your measured size and expect only minor change. Unsanforized "shrink-to-fit" denim will shrink noticeably on first wash, so you size up (commonly a size in the waist and more in length) and shrink it down to fit — a real gamble that rewards following the brand’s stated shrinkage. Confusing the two is the classic way to end up two sizes off. Check the product spec for the word "sanforized," read consensus on how a given pair shrinks, and when in doubt, buy the sanforized version for predictability.