Small Useful ToolsA little help with yarn maths

Yarn held together.
A clearer shopping list.

Changing from single to double strands—or back again? Convert the quantity in your pattern, then work out how many replacement balls to buy.

For one original yarn held consistently throughout. Calculations stay in your browser.

Example loaded: held double to single. Replace these values with yours.
In your pattern

Use the quantity for your size and the label of the original yarn. The ball weight is not the yarn’s thickness category.

455 g total held double is still 455 g of yarn, not 910 g. If the pattern is unclear, check with its designer before buying.

Your replacement yarn

One row per different yarn. For two strands of the same yarn, use one row and select 2 strands. Different colours need separate rows.

Optional extra for swatching, joins or uncertainty. 0% adds nothing; no percentage guarantees enough yarn.

Try it with an example

These demonstrate the maths, not recommended yarn pairings.

  1. One strand to two

    1,150 g at 50 m / 50 g, replaced with 150 m / 50 g held double. No extra or stash: 16 balls.

  2. Held double to single

    455 g total at 400 m / 100 g held double gives about 910 m of working length. At 200 m / 100 g held single: 5 balls.

  3. Different yarns, some already owned

    600 g at 91 m / 50 g; two replacement yarns, 10% extra and separate stash amounts: 9 additional A balls and 8 B balls.

Length first. Then whole balls.

When a pattern gives total grams, multiply by the original metres per gram, then divide by the original number of strands. That gives an equivalent working-length estimate.

When it gives grams per strand, multiply by metres per gram without dividing again. Each replacement strand needs that working length. Add your chosen allowance, subtract the usable stash for that yarn, divide by its metres per ball and round up.

Working metres = total grams × metres per ball ÷ grams per ball ÷ original strands

All lengths here are metres. One yard is 0.9144 metres. Keep the label’s weight and length paired: 400 m per 100 g is not 400 m per 50 g.

Before you buy

  • Use this only when the original is one yarn held at a constant strand count throughout. Mixed original yarns, changing sections and size adjustments are not supported.
  • Matching length does not match thickness, fibre, stretch, stitch gauge, row gauge or drape. Swatch in the actual stitch pattern and finish it as you intend to finish the project.
  • Pattern quantities and ball lengths can already be rounded estimates. Your tension, texture, joins and modifications can change use.
  • Stash must be usable yarn with the same label specification. Account for dye-lot differences and weigh yarn without packaging or cone cores.

Method references: DROPS: changing yarns and amounts and The Knitting Guild Association: yarn substitution (PDF). This tool is independent of both organisations.