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Yarn Weight and Substitution Calculator
Compare CYC yarn categories, estimate weight from wraps per inch and calculate replacement skeins by length, with an optional safety margin.
Yarn Weight and Substitution Calculator: Calculates the ceiling of pattern skeins times length per skein divided by replacement length per skein. An optional 10% margin is applied before rounding up. One yard is exactly 0.9144 metres. WPI returns all overlapping category matches. Runs 100% locally in your browser with zero server file uploads.
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Replace by length
6.6667 skeins before rounding up. One yard is exactly 0.9144 metres.
Even within the same category, fibre, construction and gauge change yarn use. Check a washed swatch; the safety margin is optional, not a guarantee.
Estimate weight from wraps per inch
Possible categories: 2 — Fine / Sport; 3 — Light / DK; 4 — Medium / Worsted / Aran
WPI is a convention, not an exact conversion. CYC publishes this guidance using industry experts, The Woolery and Ravelry; the ranges overlap. Wrap without stretching, gaps or overlaps and measure more than once.
| Category | Knit stitches | Crochet stitches | Needle mm | Hook mm | WPI convention |
|---|---|---|---|---|---|
| 0 — Lace | 33–40 | 32–42 double crochet | 1.5–2.25 | Steel 1.4–1.6; regular 2.25 | 30–40+ |
| 1 — Super Fine / Fingering | 27–32 | 21–32 | 2.25–3.25 | 2.25–3.5 | 14–30 |
| 2 — Fine / Sport | 23–26 | 16–20 | 3.25–3.75 | 3.5–4.5 | 12–18 |
| 3 — Light / DK | 21–24 | 12–17 | 3.75–4.5 | 4.5–5.5 | 11–15 |
| 4 — Medium / Worsted / Aran | 16–20 | 11–14 | 4.5–5.5 | 5.5–6.5 | 9–12 |
| 5 — Bulky / Chunky | 12–15 | 8–11 | 5.5–8 | 6.5–9 | 6–9 |
| 6 — Super Bulky | 7–11 | 7–9 | 8–12.75 | 9–15 | 5–6 |
| 7 — Jumbo | 6 or fewer | 6 or fewer | 12.75 and larger | 15 and larger | 1–4 |
CYC gauges are guidelines: stockinette for knitting and US single crochet for categories 1–7. The lace row uses US double crochet. Open lace patterns often use larger tools; follow the pattern gauge.
Sources and table dates
Accessed 2026-10-04.
Craft Yarn Council: Standard Yarn Weight System, categories 0–7. https://www.craftyarncouncil.com/standards/yarn-weight-system
Craft Yarn Council: WPI convention and measurement method. https://www.craftyarncouncil.com/standards/how-measure-wraps-inch-wpi
Category table
Craft Yarn Council, Standard Yarn Weight System, categories 0 Lace through 7 Jumbo. Gauge ranges are per 4 inches; needle and hook ranges are guidelines. https://www.craftyarncouncil.com/standards/yarn-weight-system Accessed 2026-10-04.
WPI convention
Craft Yarn Council, How to Measure Wraps Per Inch (WPI), publishes the overlapping ranges attributed to industry experts, The Woolery and Ravelry. This is approximate guidance, not a one-to-one standard conversion. https://www.craftyarncouncil.com/standards/how-measure-wraps-inch-wpi Accessed 2026-10-04.
How to use it
- Enter the pattern skein count and length per skein for both yarns.
- Select metres or yards independently, then compare weight categories and optionally add 10%.
- Read the rounded skein count; use WPI and the category table as swatching guides.
Privacy & limitations
All calculations run in your browser. Your inputs are not uploaded.
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Frequently asked questions
Is WPI an official exact conversion?
No. CYC publishes a subjective WPI guide based on industry experts, The Woolery and Ravelry. Wrapping tension affects the result, and several categories overlap.
Does matching length guarantee a suitable replacement?
No. Weight category, fibre, construction, drape and measured gauge all matter. A different category triggers a warning; even the same category needs a swatch.
Why is lace crochet different in the table?
CYC lists double crochet for lace and single crochet for the other categories, using US stitch terms. Lace patterns may need larger tools to make open fabric.
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