Yarn Weight Converter: Substitute Any Yarn Weight Accurately
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 uses the yards-per-100g ratio: new yardage = original yardage × (original yd/100g ÷ target 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.
The CYC Standard Yarn Weight System
| Weight # | Name | Yards/100g | Hook (mm) | Gauge (sc/4 in) |
|---|---|---|---|---|
| 0 | Lace | ~800 | 2.25–3.5 | 32–42 |
| 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 |
The conversion formula
New yardage = Original yardage × (Original yd/100g ÷ Target yd/100g)
Example: substituting DK (~250 yd/100g) for a worsted pattern (~200 yd/100g) that calls for 1,000 yards: 1,000 × (200 ÷ 250) = 800 yards. Wait — that's less. Re-check: you'd be using DK (thinner) in place of worsted (thicker), so the formula is actually new yardage = original × (target/original)... no, original/target. Let me reason again: you want the same physical fabric area. DK has more yards per gram than worsted because each yard is thinner. To make the same area, you need more length of DK, not less. So: new = original × (target yd/100g ÷ original yd/100g) = 1,000 × (250/200) = 1,250 yards. The calculator above uses this corrected logic.
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) is a way to identify unlabelled yarn weight. Wrap the yarn around a ruler or WPI tool without stretching or overlapping. Count wraps in one inch. Higher WPI = thinner yarn. Reference values:
- Lace: 18+ WPI
- Fingering: 14 WPI
- Sport: 12 WPI
- DK: 11 WPI
- Worsted: 9 WPI
- Bulky: 7 WPI
- Super Bulky: 5 WPI
Pro tips for yarn substitution
- Match the CYC weight category first. Substituting within the same category (worsted to worsted) is reliable. 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: pattern calls for 1,000 yards of worsted at 14 stitches per 4 inches with a 5.0 mm hook. Substitute DK: same stitches per 4 inches usually requires 4.5 mm hook. DK is thinner so total yardage shifts to ~1,150 yards (more yardage to cover the same area). Buy 5 DK skeins.
Direct answers.
How do I substitute yarn weights?
Use the yards-per-100g ratio: new yardage = original × (target yd/100g ÷ original yd/100g). Adjust the hook size to match the new weight 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. You'll need about 25% more yardage (DK is ~250 yd/100g vs worsted at ~200), and you should drop one hook size (e.g. 4.5–5.0 mm instead of 5.5–6.5 mm). The finished fabric will be slightly thinner and more drapey.
What is WPI and how do I measure it?
WPI (Wraps Per Inch) identifies unlabelled yarn. Wrap the yarn around a ruler without stretching or overlapping, count wraps in one inch. Higher WPI = thinner yarn. Worsted: 9 WPI. DK: 11. Sport: 12. Fingering: 14. It's the most reliable way to classify mystery yarn.
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
- Crochet Guild of America (CGOA) — professional standards
- Clara Parkes, The Knitter's Book of Yarn (Potter Craft) — fibre property reference
- Edie Eckman, The Crochet Answer Book (Storey) — technique reference