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Yarn Converter & Skein Planner

Metric-first yarn calculator: metres per 100 g from the label, weight to length, how many balls for a substitute yarn, and what is left of a ball. Metric first; everything runs in your browser and nothing is uploaded.

Units

1. The yarn: density from the label

2. Weight to length, length to weight

3. How many balls

The requirement is the finished length. With 2 strands you need twice that much yarn, so each strand covers half as much finished length per ball.

4. Compare with the pattern’s yarn

5. What is left of a ball

Weigh the yarn alone, without the cone, tube or label.

Extras

Yarn count converter: Nm, tex, dtex, denier, Ne
Stash combiner: total yarn from partial balls

Each row is a ball you own: its label (weight and length) and the weight left. The total is compared with the requirement in section 3.

Different yarns held together

Grams per metre of the strands add up. This is a weight and length sum, not a prediction of the fabric.

Cost

Balls always round up. Lengths round to 0.1 below 10 and to whole metres or yards above; yarn needed rounds up and yarn left rounds down. All sums are done in metres and grams, and yards and ounces are shown at the end.

How it is calculated

Every number comes from the formulas here. Calculations run in metres and grams. Imperial values are converted with exact factors: 1 yd = 0.9144 m and 1 oz = 28.349 523 125 g.

Density

  • Metres per 100 g = ball length (m) ÷ ball weight (g) × 100. Grams per metre = weight ÷ length. Example: 100 g and 200 m give 200 m per 100 g and 0.5 g/m (500 tex).
  • Weight to length: length = weight × metres per gram. Length to weight: weight = length × grams per metre. Example: 50 g of that yarn is 100 m.

Balls

  • Yarn needed = finished length × strands × (1 + margin ÷ 100). Balls = ⌈yarn needed ÷ ball length⌉. Example: 1,100 m from 200 m balls with no margin is 5.5, so 6; with the default 10% margin, 1,210 m is 6.05, so 7.
  • Strands: holding two strands together uses the yarn twice over, so the same balls cover half the finished length. 1,000 m with 2 strands and 200 m balls needs 2,000 m, which is 10 balls.
  • A requirement in grams or ounces is converted to length with the pattern yarn’s density if you entered it in section 4, otherwise with the density of the yarn above.
  • 1,200 yd from 220 yd balls is 5.45, so 6 balls without margin.

Comparison

Difference = (substitute m per 100 g − original m per 100 g) ÷ original × 100. A positive number means more metres in the same weight, so a thinner yarn. Within ±10% the yarns are called similar. This is a rule of thumb for thickness only: fibre, ply, twist and your gauge swatch decide the fabric.

Leftover

Yarn left = weight left × metres per gram. Used = ball length − yarn left.

Extras

  • Counts. tex = grams per 1000 m; dtex = 10 × tex; denier = 9 × tex (grams per 9000 m); Nm = 1000 ÷ tex (metres per gram). Ne is the number of 840-yard hanks in a pound, so Nm = Ne × 840 × 0.9144 ÷ 453.592 37 = Ne × 1.69336. Example: 20 tex is Nm 50, 200 dtex, 180 denier and Ne 29.53.
  • Stash. For each ball: weight left × (label length ÷ label weight); the total is the sum.
  • Held together. Combined g/m = sum of each yarn’s g/m; m per 100 g = 100 ÷ that sum. Two 0.5 g/m yarns give 1 g/m, or 100 m per 100 g.
  • Cost. Per 100 m = price ÷ ball length × 100; per 100 g = price ÷ ball weight × 100. You enter the price and symbol; no exchange rates are used.

Limitations

  • Label weights and lengths are nominal and vary by a few percent between dye lots; the margin covers that, and the same dye lot matters more than the maths.
  • Yarn weight category (lace to jumbo) is not looked up. The Craft Yarn Council describes its categories as approximate guidelines in gauge, not metres per gram, so a lookup would imply more precision than exists.
  • Yarn thickness depends on fibre, twist, and how much air is spun in, so equal metres per 100 g do not guarantee equal gauge. Swatch.
  • Wet or damp yarn weighs more; weigh the leftovers dry.
  • Pattern yardage is itself an estimate. For large garments or colour work, keep the default margin or raise it.

Sources

  1. NIST Guide to the SI, Appendix B.8: Factors for units listed by kind of quantity or field of science, National Institute of Standards and Technology (SP 811). Exact factors: 1 yard = 0.9144 m. The avoirdupois ounce (28.349 523 125 g) and pound (453.592 37 g) are exact by the definition of the international pound, 0.453 592 37 kg; the page itself prints the ounce rounded and marks only the yard as exact, so the ounce and pound are taken from that pound definition.
  2. Tex (unit), Wikipedia. Tex is the mass in grams of 1000 metres of yarn.
  3. Units of textile measurement, Wikipedia. Denier is grams per 9000 metres; dtex is grams per 10 000 metres; Ne (English cotton count) is the number of 840-yard lengths per pound. Nm is metres per gram by definition of the metric count.
  4. Standards & Guidelines: Yarn Weight System, Craft Yarn Council. Yarn weight categories and gauges are approximate guidelines; follow the gauge in your pattern. The planner therefore gives no weight-category lookup from metres per 100 g.

Opened and read 17 October 2026. The formulas are derived on this page and checked by unit tests.