How to Substitute Yarn in a Pattern: A Practical Guide
A practical decision guide for replacing yarn in any knitting or crochet pattern. Covers gauge matching, fiber behavior, yardage math, construction, and swatching—with a worked example.
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Yarn weight
Yarn weight calculator by wraps per inch
Measure wraps per inch (WPI) to identify and compare the matching Craft Yarn Council yarn-weight categories, with typical metric needle and hook ranges for each result.
Wrap the yarn snugly around a pencil, side by side, then count how many wraps fit in one inch.
Refine with stitch gauge (optional)
What this calculation does not account for
- WPI is subjective — results vary with how tightly you wrap. The Craft Yarn Council recommends practicing on a known-weight yarn.
- CYC WPI ranges overlap, so a value can match more than one category. The tool shows all possibilities rather than guessing.
- The CYC gauge ranges are guidelines only, and lace gauge is hard to pin down.
- WPI identifies weight, not yardage — it never converts wraps to how much yarn you need.
Last updated 1 September 2026Found a wrong number? Tell us.
How to measure wraps per inch
- Wrap the yarn around a pencil or another cylinder with a consistent circumference, for a few inches.
- Keep it snug — wraps side by side, no overlaps, no large gaps, and do not pull too tight.
- Count how many wraps fit in one inch, and measure in a few places like you would a gauge swatch.
Based on the Craft Yarn Council's Wraps Per Inch guide and Standard Yarn Weight System.
Compare yarn weight categories by WPI
Use the chart to compare the numbered Craft Yarn Council categories. WPI ranges overlap, so one measurement can match more than one category; the calculator keeps every match visible instead of forcing a single answer.
| CYC category | WPI range | Typical knitting needles | Typical crochet hook |
|---|---|---|---|
| 0 · Lace | 30+ | 1.5–2.25 mm | Steel 1.6–1.4 mm |
| 1 · Super Fine | 14–30 | 2.25–3.25 mm | 2.25 mm |
| 2 · Fine | 12–18 | 3.25–3.75 mm | 2.25–3.5 mm |
| 3 · Light | 11–15 | 3.75–4.5 mm | 3.5–4.5 mm |
| 4 · Medium | 9–12 | 4.5–5.5 mm | 4.5–5.5 mm |
| 5 · Bulky | 6–9 | 5.5–8 mm | 5.5–6.5 mm |
| 6 · Super Bulky | 5–6 | 8–12.75 mm | 6.5–9 mm |
| 7 · Jumbo | 1–4 | 12.75+ mm | 9–15 mm / 15+ mm |
These category-level ranges are typical starting points in millimetres, not needle or hook size-system conversions. Follow your pattern and confirm the fabric with a swatch.
Sources:Craft Yarn Council WPI guideandStandard Yarn Weight System.
Continue with a related calculator
Use the Yarn Estimator for quantity or the Gauge Calculator for a measured swatch. Neither job is the same as converting needle or hook size systems.
Learn the method
Guides for this calculator
How to Measure Wraps Per Inch (WPI)
A step-by-step guide to measuring wraps per inch consistently, with troubleshooting for common errors and honest limits of what WPI can tell you.
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Yarn Weight Guide: Understanding Categories, Labels, and When to Substitute
Learn how yarn weight categories work, why the same yarn can have different names, and how to read labels for confident substitution.
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How Much Yarn Do I Need? A Practical Planning Guide
A practical guide to estimating yarn yardage: understand the variables that affect quantity, read yarn labels correctly, and know when to use a calculator for precise results.
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