Skip Navigation Website Accessibility

Swapping Yarn Weights

17 Jul 2022

Colorful yarn organized by color

This pattern calls for DK weight yarn, can I substitute Aran? Can I substitute a fingering weight for a sport weight?

Yarn weights from 1 to 7

Every week someone asks us that all important question.  The answer is … it depends.  

In general, if the pattern calls for fingering/DK/Aran, then stick with the weight called for in the pattern.  The designer wrote the pattern for that yarn weight, calculated stitches, and rows per inch for that yarn weight and specified what needles to use.  There is a reason she made those decisions. 

As a designer, you have a vision of what your piece will look like, and based on that vision, you design it.   Let’s consider a shawl pattern first:

The designer envisions drape, fluidity, lacy texture, something light enough to wear in the summer with a sundress.  So right off she’s thinking fingering or lace weight yarn, in a linen/cotton/silk blend.  She writes the pattern; tests it on yarn to make sure its correct; changes the yarn or design, if needed, so that it looks like her vision, and then publishes it.

You, the knitter, fall in love with the pattern and can’t wait to cast on.  Your LYS doesn’t have the exact yarn, but they have something similar.  If the weight is the same and the content is similar – cast on and enjoy your knitting.  If it’s a thicker yarn it will not have the drape of the thinner yarn, plus you will have to change your needle size according to the yarn weight.  When you start changing needle sizes, you also change the final dimensions of the end project.  The shawl you fell in love with won’t look like what you’ve knitted. (I’ll discuss makeup of the yarn in another article). 

Conversely, a sweater might be designed for warmth and to keep out the elements.  The designer decides to use an Aran weight wool at a tight tension.  She will choose a stitch pattern that reflects her goal.  If you try to use a smaller weight yarn, the sweater won’t stand up to the winter conditions and you won’t be happy or warm, when you put it on. There is no way you will be able to knit the pattern, as written, with a completely different weight of yarn.

What happens when you substitute yarn weights?   Tension becomes an issue, plus you now must guess what size needle to use.  All the directions have been written for a certain gauge, the charts reflect that gauge, and sizing reflects that gauge.  Yarn weight is the single most important step towards getting your tension and gauge correct for the pattern.

Yarn weights organized from lace, super fine, fine, light, and medium to bulky and super bulky.

Next time I’ll discuss yarn content and how it affects your final project.  Eventually, I’ll explain how to break the rules, but for now it’s best to follow them!!!


  • Tue - Thur 11am -5pm
  • Friday 11am - 4pm
  • Saturday - 10am - 3pm
  • Closed Sunday and Monday

Find Us