Yarn Weight Converter: Compare Categories, WPI and Yardage
Pick your original yarn weight and the weight you want to substitute. Enter the original pattern's yardage. The calculator returns the adjusted yardage, the new hook size, and the expected gauge change.
Yarn weight conversion scales the yardage by the ratio of yards per 100 g: new yardage = original yardage × (target yd/100g ÷ original yd/100g). Going lighter (e.g. worsted to DK) means more yards needed; going heavier means fewer. Always re-swatch with the substitute yarn before committing — fibre and tension affect the result.
Classification asks what weight category a yarn belongs to. That is what the Craft Yarn Council system answers, what wraps per inch estimates, and what this converter works with. Substitution asks whether one yarn can replace another in a specific pattern. Sharing a category makes two yarns candidates for substitution; it does not make them equivalent. Ply, twist, fibre and yards per 100 g all vary within a single category, and a swatch is the only thing that settles it.
The CYC Standard Yarn Weight System
| Weight # | Name | Yards/100g (not CYC) | Hook (mm) | Gauge / 4 in (sc unless marked) |
|---|---|---|---|---|
| 0 | Lace | ~800 | 1.4–1.6 steel, or 2.25 regular | 32–42 dc |
| 1 | Fingering / Sock | ~400 | 2.25–3.5 | 21–32 |
| 2 | Sport | ~300 | 3.5–4.5 | 16–20 |
| 3 | DK / Light Worsted | ~250 | 4.5–5.5 | 12–17 |
| 4 | Worsted / Aran | ~200 | 5.5–6.5 | 11–14 |
| 5 | Bulky / Chunky | ~150 | 6.5–9 | 8–11 |
| 6 | Super Bulky | ~100 | 9–15 | 7–9 |
| 7 | Jumbo / Roving | ~60 | 15+ | ≤6 |
Two of these columns are the Craft Yarn Council's: the crochet gauge ranges and the recommended hook ranges, reproduced as published. The yards-per-100 g column is not. The Council does not publish yards per 100 g for its categories, and no standard does — length per unit mass depends on fibre density as well as thickness, so it varies between two yarns in the same category. Those figures are CrochetCalc's working reference values, used to drive the estimate above and shown here so you can see what the result rests on. Category 0 is the only row where the Council lists two hook entries rather than a range, and the only row measured in double crochet rather than single.
The conversion formula
New yardage = Original yardage × (Target yd/100g ÷ Original yd/100g)
The direction follows from the fabric rather than from the label. You are covering the same physical area either way, and a thinner yarn covers less ground per yard, so it takes more length to fill that area. Substituting DK for a worsted pattern that calls for 1,000 yards: DK carries more yards per 100 g than worsted because each yard is thinner, so the estimate is 1,000 × (250 ÷ 200) = 1,250 yards — more than the original, not less. The calculator above returns this figure.
Treat that number as a first approximation rather than a requirement. The yards-per-100 g figures it rests on are this site's working reference values, not published data, and real yarns scatter widely around them — a DK acrylic can run 322 yards per 100 g against the 250 assumed here. The approximation is closest between neighbouring categories and loosest at the ends of the scale. Swatch, then buy.
The maths gives you the starting point. Fibre content (cotton vs wool vs acrylic), twist, and ply all affect the final gauge. Make a swatch with the substitute yarn at the target hook size before buying enough for a full project.
What is WPI?
Wraps per inch (WPI) identifies the weight of an unlabelled yarn by measuring it. Wrap the yarn around a ruler or WPI tool so the strands touch without being stretched or overlapped, then count the wraps that fall inside one inch. Higher WPI means thinner yarn. The Craft Yarn Council publishes WPI as ranges rather than single values, and the ranges overlap:
| Category | Name | Wraps per inch |
|---|---|---|
| 0 | Lace | 30–40+ |
| 1 | Super Fine (fingering, sock) | 14–30 |
| 2 | Fine (sport) | 12–18 |
| 3 | Light (DK) | 11–15 |
| 4 | Medium (worsted, aran) | 9–12 |
| 5 | Bulky (chunky) | 6–9 |
| 6 | Super Bulky | 5–6 |
| 7 | Jumbo | 1–4 |
Because the ranges overlap, a reading of 12 wraps is consistent with Fine, Light and Medium, and the Craft Yarn Council notes that the result varies with how tightly you wrap. Treat WPI as a way to narrow the field when a yarn has no ball band, then confirm the choice with a gauge swatch rather than treating the number as a classification. The wraps per inch calculator does that lookup for you and reports every range a reading falls inside.
From category to substitution: what the category has not told you
- Match the CYC weight category first. Staying inside one category is the best starting point, but it is a shortlist rather than a guarantee: two worsted yarns can differ in ply, twist, fibre and yards per 100 g, and those differences change gauge and drape even when the category matches. Crossing categories requires gauge adjustment.
- Check yards per ounce, not just weight category. Two worsted yarns at the same category can have different yards-per-ounce.
- Make a new swatch with the substitute. Different brands and fibre contents produce different gauges even at the same nominal weight.
- Consider fibre behaviour. Cotton substituted for acrylic produces firmer, less stretchy fabric. Pick substitutes whose fibre behaviour matches your project's needs.
- Buy 10-15% extra of the substitute. Substitutions almost always require slightly different yardage than the original.
Worked example
Substituting DK for worsted: a pattern calls for 1,000 yards of worsted worked at 14 stitches per 4 inches, which the Council's range puts on a 5.5 mm hook. Holding that same stitch count in DK usually means dropping to about 4.5 mm. DK is thinner, so covering the same area takes more length — the calculator returns 1,250 yards. Buy to that figure, add the usual margin for a substitution, and swatch first: the category sets the shortlist, not the answer. How many skeins that is depends entirely on the ball band in front of you, which is why this page does not guess it.
Common mistakes when converting yarn weights
These are the errors that most often send a calculated result off course. Each one changes the number the calculator gives you.
-
Treating category names as exact.
DK, light worsted and 8-ply overlap but are not identical, and brands place themselves differently within a category. Use the category to shortlist, then compare wraps per inch and stated gauge.
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Assuming equal weight means equal yardage.
Fibres differ in density. 100 g of cotton carries considerably less length than 100 g of acrylic at the same thickness, so a like-for-like substitution by ball weight can leave you short.
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Ignoring ply construction.
Two yarns can match on weight and gauge and still behave differently. A tightly plied yarn shows stitch definition; a singles yarn blooms and blurs it.
Frequently asked questions
How do I substitute yarn weights?
Scale the yardage by the ratio of yards per 100 g: new yardage = original × (target yd/100g ÷ original yd/100g). Those per-category yardage figures are working assumptions rather than published standards, so the result is an estimate. Adjust the hook size to match the new category, and swatch before committing — fibre and tension affect the result.
Can I use DK yarn instead of worsted?
Yes. DK is one step lighter than worsted. Expect to need roughly 25% more yardage — that figure comes from this site's working values of ~250 yd/100 g for DK against ~200 for worsted, not from a published standard — and to drop a hook size, from the Council's 5.5–6.5 mm range for worsted to its 4.5–5.5 mm range for DK. The finished fabric will be slightly thinner and more drapey. Sharing a step on the scale does not make the two yarns interchangeable; swatch the DK before you buy for the whole project.
What is WPI and how do I measure it?
WPI (wraps per inch) helps identify unlabelled yarn. Wrap the yarn around a ruler without stretching or overlapping and count the wraps inside one inch; higher WPI means thinner yarn. The Craft Yarn Council publishes overlapping ranges rather than single values — Medium (worsted) 9–12, Light (DK) 11–15, Fine (sport) 12–18, Super Fine 14–30 — so one reading often fits more than one category, and the result varies with how tightly you wrap. Use WPI to narrow the field on a mystery yarn, then confirm with a gauge swatch.
What happens if I use the wrong weight?
Two things: dimensions change (lighter yarn produces smaller pieces; heavier yarn produces larger pieces at the same stitch count), and yardage requirements change. For garments this is critical — wear the wrong weight and the sweater won't fit. For blankets it's less critical because the final size can vary.
Can I hold two strands together instead?
Yes — a useful substitution trick. Two strands of DK held together approximate worsted weight. Two strands of fingering approximate DK. The fabric won't be identical to single-strand at the heavier weight (it tends to be slightly less drapey) but it's a workable substitute when you only have the lighter yarn.
Sources & further reading
- Craft Yarn Council — Standard Yarn Weight System — the categories 0–7, their gauge ranges and recommended hook sizes.
- Craft Yarn Council — How to measure wraps per inch — the WPI method shown in the diagram above.
- Craft Yarn Council — Standards FAQs — on how the categories are intended to be used.
The Craft Yarn Council system classifies yarn by thickness. It does not certify that two yarns in a category are interchangeable, and no standard does — ply, twist, fibre and yards per 100 g all vary inside one category. WPI values are approximate identification aids, not defined thresholds.