Yarn held together calculator

Holding two or more strands together makes a thicker yarn: two strands of fingering behave roughly like DK. It is a good way to use a stash, blend colours or make a sturdier fabric. This calculator works out the combined length per 100 g and wraps per inch, the yarn weight category it matches, a hook range to start with, and how much of each strand to buy.

How to use the calculator

1. Enter each strand's length and weight per ball from its label: two strands, or three.
2. Optionally enter each strand's wraps per inch (WPI).
3. Optionally enter the length the pattern needs, to see how many balls of each strand to buy.

How the calculator works

Weights add up along the strand: every metre of combined yarn contains a metre of each strand. So the combined weight per metre is the sum of each strand's weight per metre, and the combined length per gram is one over that sum:

Combined length per gram = 1 ÷ (weight₁ ÷ length₁ + weight₂ ÷ length₂ + …)

Thickness adds by cross-section, like the areas of circles, so wraps per inch combine like this:

Combined WPI = 1 ÷ √(1 ÷ WPI₁² + 1 ÷ WPI₂² + …)

The combined length per 100 g is matched to the Craft Yarn Council weight categories (using WPI if the length does not give a category), and the category's usual hook range is suggested as a starting point.

Reading your results

• Combined length per 100 g: in your units, with the other unit underneath.
• Combined wraps per inch: shown when every strand has a WPI.
• Behaves like: the yarn weight category, and a starting hook range in the notes. If length and WPI point to different categories, the calculator says so.
• What to buy: the length and balls of each strand. Every strand runs the full length.

Worked example

Two strands of fingering yarn, each 400 m per 100 g and 16 wraps per inch, for a pattern that needs 800 m of DK.

• Combined: 1 ÷ (100 ÷ 400 + 100 ÷ 400) = 2 m per gram, or 200 m per 100 g.
• WPI: 1 ÷ √(1/16² + 1/16²) = 11.3.
• That is the 3 Light (DK) category, with a starting hook range of 4.5 to 5.5 mm.
• Buy 800 m of each strand: two 100 g balls of each, four in all.

The same strands labelled 400 yd per 100 g are a little thicker (they combine to 200 yd, which is 183 m, per 100 g), and the calculator puts them in 4 Medium.

Accuracy and limits

• This is a modelled estimate, and our automated tests check the arithmetic. Yarns do not pack perfectly round, so the fabric may come out a little thicker or thinner.
• Fluffy strands such as mohair add loft without much weight, so the fabric can look and behave thicker than the numbers suggest.
• The combined WPI is skipped unless every strand has one.
• No extra is added to the amounts to buy.
• Swatch with the suggested hook range before you start.

Common mistakes

1. Buying half the length of each strand. For 800 m of combined yarn you need 800 m of each strand, not 400 m.
2. Catching only one strand. With two thin strands it is easy to miss one. Keep both feeding evenly, for example from two bowls, and check the stitches as you go.
3. Making stiff fabric. Two dense cotton strands make a firm fabric, good for baskets and bags; go up a hook size for anything that should drape.

Tips for more accurate results

• To hold one ball double, wind it into a centre-pull cake and use the inside and outside ends together, or weigh it and wind half into a second ball.
• Use the yarn substitution calculator to compare the combined yarn with the one in your pattern.

Frequently asked questions