Yarn labels describe thickness with words — lace, fingering, sport, worsted, bulky, super-bulky — and the words drift between brands like weather. The honest tool costs nothing: WPI, wraps per inch. Wrap the yarn snug around a pencil for one inch, count the wraps.
Under 8 wraps is bulky. 10–12 is worsted. 14 and up is fine. That line is the whole mystery: two "worsted" skeins from different shelves can behave differently, but both will wrap the same if they actually are the same — and a band warp planned on wrapping truth, instead of labeling hope, packs the way the pattern expects.
The other secret in the learn page's yarn section is the cone. Yarn sold on cones is usually the same fiber at a fairer price — and cones are what rug craft really runs on, which goes by the mile rather than the skein. The app's supplies lists speak in the units your shop actually sells — meters and yards, with take-up and loom waste already counted in — so "almost enough" stays out of the basket.
Wrap a pencil, warp a band this week. — the bench crew