Knitting & crochet calculator
WPI (Wraps Per Inch) to Yarn Weight Converter
Wrap your mystery yarn around a ruler for exactly one inch, count the wraps, and enter that number here to get its yarn weight category and a suggested needle or hook size range.
Wraps per inch (WPI) is a simple way to identify an unlabeled or hand-spun yarn's weight category when you don't have the original ball band. Wrap the yarn snugly (not stretched, not loose) around a ruler or WPI tool for exactly one inch, counting each individual wrap, then look up that count here.
The result maps your wraps-per-inch count to the standard yarn weight system (lace through jumbo) and gives you a starting needle or hook size range based on the Craft Yarn Council's standard recommendations for that weight.
Worked example: 11 wraps per inch typically corresponds to a medium (worsted) weight yarn, suited to roughly 4.5-5.5mm needles or 5.5-6.5mm hooks.
Frequently Asked Questions
How tightly should I wrap the yarn for an accurate count?
Snugly enough that there are no gaps between wraps, but not stretched. Over-stretching the yarn will inflate your wrap count and make the yarn look thinner than it is.
Is WPI more reliable than reading a ball band?
A ball band is more reliable when you have one. WPI is a good fallback for unlabeled, hand-spun, or hand-dyed yarn where the manufacturer's weight category isn't available.
Why is the needle/hook range so wide for some weights?
Needle and hook size also depends on the fabric density you want - a tighter fabric for structure uses a smaller size within the range, while a drapier fabric uses a larger one.
Does fiber content affect WPI-to-weight accuracy?
Slightly. Very elastic fibers (like some wools) or very inelastic ones (like linen) can wrap a bit differently than the averages this chart is based on, but WPI is still a solid starting estimate for any fiber.