WPI to Yarn Weight Converter
Last updated: March 2026
Enter your wraps per inch and instantly identify yarn weight, recommended needles and hooks, gauge range, and suggested projects.
Why You Need a WPI Calculator
You have found a gorgeous skein at a yard sale, inherited a bag of unlabeled yarn from a fellow crafter, or peeled off a ball band only to lose it before starting your project. Now you are holding mystery yarn with no idea what weight it is. Wraps per inch (WPI) is the fastest and most reliable way to identify it.
WPI measurement is a technique every fiber artist should have in their toolkit. It requires nothing more than a ruler and a few seconds of your time, yet it gives you the information you need to select the right needles, hooks, and patterns for any yarn in your stash. This calculator takes your WPI reading and instantly maps it to the Craft Yarn Council weight system with all the details you need to start crafting.
What Is Wraps Per Inch?
Wraps per inch is a standardized measurement of yarn thickness. You wrap the yarn around a ruler, dowel, or dedicated WPI tool for exactly one inch, keeping wraps snug and side by side without overlapping or stretching. The number of wraps that fit in that inch tells you the yarn's relative thickness.
Thinner yarns produce more wraps per inch — lace weight yarn wraps 30 or more times in an inch, while jumbo yarn may only wrap 1 to 4 times. The Craft Yarn Council has established WPI ranges for each of the eight standard yarn weight categories (0 through 7), giving crafters a universal reference for identifying unlabeled yarn.
It is important to understand that WPI ranges overlap between adjacent weight categories. A yarn that measures 12 WPI could be a tightly plied sport weight or a loosely spun worsted. This overlap is normal and reflects the natural variation in yarn construction. When your measurement falls in an overlap zone, the only definitive way to confirm the weight is to swatch and compare your stitch count against the standard gauge ranges.
How the WPI Converter Works
The converter uses the Craft Yarn Council's official WPI ranges to map your measurement to one or more yarn weight categories. Each category has a defined WPI range: Lace is 30 and above, Super Fine is 14 to 30, Fine or Sport is 12 to 18, Light or DK is 11 to 15, Medium or Worsted is 9 to 12, Bulky is 6 to 9, Super Bulky is 5 to 6, and Jumbo is 1 to 4.
When your WPI falls within a single category, the converter displays that weight with its corresponding needle sizes, hook sizes, gauge range, typical yardage per 100 grams, and suggested project types. When your WPI falls in an overlap zone — for example, 12 WPI matches both Fine/Sport and Medium/Worsted — the converter shows all matching categories and recommends swatching to confirm which weight best describes your yarn's behavior.
The recommended needle and hook sizes come directly from the Craft Yarn Council's published standards. The yardage estimates are typical values across common fiber types, though actual yardage varies by fiber content — cotton is heavier per yard than wool, and silk is heavier than alpaca.
Wrap your yarn around a ruler for one inch without stretching or overlapping. Count the wraps to find your WPI.
WPI Reference Chart
| Weight | CYC | WPI | Needles | Hooks | Gauge | Yds/100g |
|---|---|---|---|---|---|---|
| Lace | 0 | 30+ | US 000–1 | B/1–E/4 | 33–40 sts/4″ | ~800 yds |
| Super Fine | 1 | 14–30 | US 1–3 | B/1–E/4 | 27–32 sts/4″ | ~400 yds |
| Fine / Sport | 2 | 12–18 | US 3–5 | E/4–7 | 23–26 sts/4″ | ~300 yds |
| Light / DK | 3 | 11–15 | US 5–7 | 7–I/9 | 21–24 sts/4″ | ~250 yds |
| Medium / Worsted | 4 | 9–12 | US 7–9 | I/9–K/10.5 | 16–20 sts/4″ | ~200 yds |
| Bulky | 5 | 6–9 | US 9–11 | K/10.5–M/13 | 12–15 sts/4″ | ~130 yds |
| Super Bulky | 6 | 5–6 | US 11–17 | M/13–Q | 7–11 sts/4″ | ~80 yds |
| Jumbo | 7 | 1–4 | US 17+ | Q+ | 6 and fewer sts/4″ | ~40 yds |
WPI ranges overlap between adjacent weights. Swatching is the most reliable way to confirm yarn weight.
How to Measure WPI
- Use a ruler or WPI tool. Wrap yarn snugly around it for exactly one inch.
- Don't stretch the yarn. Let the wraps sit naturally side by side without gaps or overlapping.
- Measure in multiple spots. Yarn thickness can vary along the skein — average 2\u20133 readings for accuracy.
- Plied yarn can be tricky. Highly textured or boucl\u00E9 yarns may not wrap evenly — swatch for the best results.
How to Use the WPI Calculator
Start by measuring your yarn. Hold a ruler horizontally and wrap the yarn around it without stretching, pulling, or overlapping. Each wrap should sit snugly against the last, touching but not compressed. Count the wraps in exactly one inch. For the most accurate reading, measure in the middle of the ruler where edge effects are minimal.
For handspun or textured yarn, measure in two or three different spots along the skein and average the results. Handspun thickness can vary, and averaging gives a more representative WPI. For plied yarns, wrap the plied yarn as it comes — do not separate the plies.
Enter your WPI count into the calculator. The tool displays your matching yarn weight category (or categories if you are in an overlap zone) along with recommended needle sizes in US and metric, hook sizes in US letter and metric, the standard gauge range in stitches per 4 inches, typical yardage per 100 grams, and project suggestions suited to that weight.
Understanding Your Results
If your WPI matches a single weight category, the results are straightforward — use the recommended needle or hook size as a starting point and swatch to confirm your gauge. If you see multiple categories, your yarn sits in an overlap zone and could work as either weight. Swatch with needles for both categories and decide which fabric you prefer.
The yardage per 100 grams is an average across common fibers. Wool and acrylic yarns tend to fall near the typical value, while cotton and linen yarns yield fewer yards per 100 grams due to their higher density. Silk falls in between. Use the yardage estimate as a planning guide, not an exact figure.
Pro Tips
From 30+ years of fiber arts experience
- ✓Wrap on a smooth surface like a pencil, dowel, or knitting needle rather than a flat ruler — the wraps sit more naturally and give a more accurate count.
- ✓Do not push wraps together or spread them apart. The natural resting position of the yarn is what you want to measure.
- ✓If your WPI falls right on a boundary (like exactly 9 WPI between worsted and bulky), swatch with both the lighter and heavier weight needle suggestions. The fabric you prefer determines which category to treat the yarn as.
- ✓Keep a WPI cheat card in your yarn stash for quick reference at fiber festivals and thrift stores. Knowing your WPI ranges lets you evaluate mystery yarn on the spot.
References & Standards
- Craft Yarn Council — Yarn Weight System — Industry-standard yarn weight categories and gauge ranges
- Craft Yarn Council — Needle & Hook Sizes — Standard sizing charts for knitting needles and crochet hooks
- Ravelry — Yarn database, pattern library, and community for fiber artists
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Frequently Asked Questions
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