Why yarn weight matters in knitting. How to knit with any yarn weight

Yarn weight and why it matters

In this blog post I'm talking all things yarn weight and why it matters. Knitting or crocheting with whatever yarn you have to hand may be an option for you if you just want to make something without a pattern but that will not be the case for other things. Getting the yarn weight right is vital for success in knitting. 

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Here's why yarn weight matters in knitting. Knitting with the wrong yarn weight or needle size will dramatically alter your project

If you're knitting something with a pattern, it is very helpful to use the yarn weight suggested and here's why: 

  • Thickness of yarn will affect the finished look. 
  • Meterage is usually lower the thicker the yarn meaning you may need more than you thought. 
  • The drape of the final fabric varies. 
  • The size of the finished project will vary. 
  • The needle or hook required may not match. 

If you only have 4mm needles and want to use a chunky yarn, you're going to end up with a really dense, stiff piece of fabric. That will not work if you're wanting to wear it, for example. 

Do I have to use exactly the same yarn as the pattern states? 

No, you don't. Every knitter has a budget unique to them and there is a lot of personal preference to fibre types anyway, so don't ever feel that you have to use exactly the same yarn. Yarns come and go and get discontinued frequently (especially commercial yarns) so by the time you come to knitting from a pattern, it may not be available anyway! 

You can read more about how to substitute yarn here.

Do I need to have more than one pair of needles? 

Yes. I would tell every knitting beginner to invest in a needle range of 3mm-10mm  (US3-US15) purely because you'll come across a range of requirements. Even a DK cardigan or hat pattern that asks for 4mm needles will want you to also have some 3.25mm for the ribbing of the cuffs and button bands. 

Have more than one pair of needles so that you can match them to the yarn you have. If someone has kindly sent you away with a bundle of gift yarn to help you get started, you're going to need to anticipate the requirement for different needle sizes. 

Needle sizes ensure that the gauge swatch is correct. This is also referred to as tension in knitting patterns. 

How to do a gauge swatch

To do a gauge swatch, take the needles that are recommended by the pattern and take yarn in the size recommended by the pattern. 

Knit at least the amount that the pattern states. Ideally, you should knit a few more stitches so that you're measuring more than just the very outer edges of the square. If the tension is stated as "22 sts by 30 rows" I would cast on and knit 30 stitches and 35 rows just to make sure that I can measure it accurately with a standard knitting gauge ruler like this one here. 

Pony knitting gauge ruler. How to check yarn weight and measure your tension for knitting

If you struggle to get an accurate gauge measurement from measuring with tape or a ruler, you can always use a knitting gauge such as this Knitpro one here.

Knitpro needle gauge for knitters. Measure knitting tension accurately with a knitting gauge.


Your swatch will probably curl up and misbehave at first. What some designers recommend is blocking the swatch to measurements. This is really handy for learning about how your yarn will behave when the item has been washed. You won't notice much of a difference with synthetic yarns but I would certainly recommend this method for natural fibres or synthetics that are blended with natural fibres. 

Your gauge swatch tells you a few things: 

  1. It tells you whether you're using the right needle size. 
  2. It tells you if you're using a yarn thick or thin enough. 
  3. It shows you how much yarn you'll eat up per inch. 
  4. It gives you an idea of how the finished item will look if you knit it in that yarn. 
  5. It gives you a chance to see how the yarn will behave after washing. 

If your stitches and rows are off, there are some solutions: 

If you have more stitches and rows than the tension on the pattern, you need to go up a needle size. You can start by going up by 0.5mm and work your way from there. 

If you have fewer stitches and rows than the tension on the pattern, you need to go down a needle size. As with the previous instruction, do this by 0.5mm increments. 

Good reasons to swatch your knitting before starting a project. Why swatching is important for yarn weight

Does it matter if my stitches are the right size? 

Your gauge swatch will tell you if what you're making will actually fit you or be the size it is supposed to be. If you knit a toy rabbit in 6mm needles and chunky yarn but the pattern calls for 3.5mm needles and DK yarn, you're going to end up with a much bigger rabbit that requires much more yarn! 

Many knitters will say they don't swatch and that they don't mind if the finished item and that's their choice but as a designer I can assure you that dp=oing a swatch saves so much time, hassle and questions. If you're also a beginner, it's another practice square before the big event! 

So in conclusion, no, you generally can't just use any yarn weight unless you've got a really clever pattern that allows you to knit in any weight. These patterns will have several tensions in the pattern so the chances of you meeting at least one of them are high! This isn't common practice though and won't work for everything. 

Understanding yarn weights. How yarn weight and needle size can affect your project

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