Knitting Yarn Guide: Types, Weights, and How to Choose the Right One

March blog post title

So you find yourself in the yarn shop again looking through the shelves, trying to find the ‘perfect’ yarn for your latest  knitting or crochet project, after you realise they don’t have the yarn the pattern calls for. You feel stuck, not entirely sure if the yarn you have your eye on will do the job.

Choosing the right yarn for your project can feel daunting, but today on the blog I want to help by giving you some tips that I find help me. The tips I’m sharing here apply equally to knitting or crochet yarns.

Why ‘types’ of knitting or crochet yarn matter

The type of yarn you choose for your project will make a huge difference in how your final project works up. Let’s look at some basic facts about yarn types that will affect your choice.

Fibre Content

Different yarns will be made using different fibres, sometimes blended, and sometimes pure. These fibres are usually based on either animal, plant or man made materials.

Common animal fibres used in yarns include:

  • wool
  • mohair
  • cashmere
  • angora
  • alpaca
  • silk

Plant fibres you will regularly see used in yarns include:

  • cotton
  • bamboo
  • tencel
  • linen – often used as a blend

Common man made fibres used in yarns include:

  • polyester  – usually used as a blend
  • nylon – regularly used as a blend
  • acrylic

Every fibre base will have characteristics that make it different from another, even within the same group. For example silk has a beautiful sheen and moves fluidly once knit. It drapes the body, making it perfect for evening pieces, especially accessories like shawls. However, it can also stretch over time, making it a poor choice for sweaters, unless it is heavily blended with something like wool.

Let us have a little look at each of the more commonly-found fibres and their uses.


Wool is fibre from the fleece of a sheep. It is warming, durable and resistant to moisture, which makes it a great choice for colder months. There are some breeds like Merino and Bluefaced Leicester which can be worn all year around. Some wools (depending on the breed) can be harder to wear against the skin than others, because some wools come from a double coated breed and guard hairs can feel prickly. Those types of yarn are better for bags, or hats, whereas a beautifully soft Merino is highly recommended for garments worn next to the skin. Wool is usually fairly inexpensive, depending on the breed and by comparison to other animal alternatives.


Mohair is a fluffy fibre, which has a beautiful sheen to it. It is much more elastic than wool, which is great for resisting creases but that makes it prone to stretching. You will therefore often find it either blended with a wool fibre, or recommended for lighter accessories, rather than garments.


Cashmere is an expensive yarn, but is beautifully soft to wear, making it a wonderful choice for luxury knits. It has a warming effect and a ‘cloud-like halo’, which means it is slightly fluffy to the eye. Cashmere is also prone to stretching, which is why you will often find it heavily blended with wool, like Merino.


Angora is the fur of a rabbit and so as you can imagine it is light, soft and fluffy to wear. A great option for luxury accessories. Not unlike mohair (although much finer) you will often find it blended with wool, because of its elasticity and cost.


Spun from the fleece of alpaca, this fibre is known to be hypoallergenic. This is why it is often used in next-to-skin garments and baby clothes. It can stretch, so like most other animal fibres you will often find it blended with the sturdiness of wool.


Soft, smooth and lustrous, silk is an expensive fibre. It is usually put in the plant fibre category, but is actually made by silkworms who digest either cultivated or wild Mulberry leaves and create the fibre we wear in their cocoons. It is beautiful as knitted lace and adds drape when blended with other fibres (mostly animal) for garments and shawls.


Cotton is thought as the most commonly used plant fibre and as it is widely grown, it is fairly inexpensive compared to most other plant based fibres. It is very inelastic because of the short length to the fibres, which gives the yarn a smooth finish. This allows for really great stitch definitions, but not much elasticity. Due to this, it can be known to split during knitting, especially in larger projects where the weight of a project pulls down on the working stitches.


Bamboo is fast becoming popular as an alternative to cotton and because it is easy to grow, we are seeing more use of this yarn by yarn manufacturers. It has a good stretch, which is great for smaller projects, but needs to be considered for those larger garments.


This fibre is made from wood pulp from eucalyptus trees, and is used increasingly in clothing manufacture. Tencel yarn is similar to bamboo; it is smooth and soft, with a wonderful silk-like drape and sheen. It is a strong yarn which is comfortable to wear against the skin.


Linen is a sturdy plant fibre, much more dense and unforgiving than cotton, but it does make a lovely blend for summer, because of its moisture-wicking capabilities. It is usually mixed with other plant based fibres to soften the resulting yarn.


This is a synthetic, or man made fiber and often blended with wool for sock yarn. Its elasticity makes it perfect for allowing socks to stretch over your feet and create ease in movement. 


Polyester is usually blended with animal or plant fibres to help with drape and ease of care. It is much more inexpensive by comparison to natural alternatives, so has become more popular in recent years.


The most commonly used man made fibre has to be Acrylic. It is inexpensive and easy to care for, making it a great choice for those on a budget. But it can stretch and have a crunchy feeling which isn’t always great during wear. Long term a wool alternative will outperform every time.

A word on yarn ply

Yarn ply refers to the number of single lengths of spun yarn twisted together to make a skein of yarn. Traditionally knitting yarns would be either 2, 3, or 4 ply, but you can have as many as 6, or even 8. Some skeins have just one single ply.

Typically the more plies a yarn has, the more rounded and firm the overall plied yarn becomes, making a better stitch definition. However, fibre content can have an affect on this. For example, a mohair yarn would have less stitch definition than a wool yarn, because of the ‘fluff’ of the mohair fibre.

Why ‘weights’ of knitting yarn matter

Let us look at weights of yarn next. ‘Weight’ in this case refers to the thickness, or gauge of a knitting yarn (otherwise known as ‘wraps per inch’). Typically, there are only a few ‘weights’ of yarn you will choose for most projects, but it is worth discovering all of your options.


Great for lighter garments, usually shawls, lace weight is the finest yarn you can buy. It is usually knit on 2.00mm – 2.50mm needles or hooks.


Great as an all round yarn, you can make anything from socks, hats and shawls to lightweight garments. It is usually knit on 2.50mm – 3.5mm needles or hooks.


Originally an American weight, sport weight yarn sits somewhere between a 4ply and a double knit (in the UK we might call it 5ply) and depending on the fibres it can be a great all rounder yarn. It is usually knit on 3mm – 3.50mm needles or hooks.


This is probably one of the most commonly used yarn weights for garment knitting and is usually knit on 4mm needles or hooks.


We are getting into those heavier winter knits now with Aran weight yarns. These are usually worked on 5mm needles or hooks.


Chunky (and superchunky) is a term of a weight of yarn thicker than Aran weight and can vary widely from yarn used on needle size 6mm and above, to finger knitting yarn. It is generally used for accessories, purely because the length of yarn per skein would require a much bigger expense for larger garments.

Different weights of yarn have different lengths, for example there will be a much longer length of finer yarn in a laceweight than in a 4ply yarn.

The combination of yarn length and thickness will make a huge difference to your project when substituting yarns.

How to select the perfect knitting yarn for your project

Typically, if you are searching for a specific knitting yarn for your next project, it is because you already have a pattern in mind. So my best advice is to start with that pattern. Let me show you how I make my yarn substitutions:

Step 1 – Find out what the details of the original knitting yarn

The easiest place to start is to find out exactly what the pattern calls for in yarn and note down its:

  • fibre content – note down the percentages if it is a blend
  • weight – eg 4ply, DK
  • length per ball or skein – for example 400metres per 100grams
  • ply if they have this
  • suggested needle size
  • gauge
  • care instructions

This will immediately give you a guide to follow for substitution purposes. Google is a great tool to use to find this information directly from manufacturer sites, as are knitting community sites like Ravelry

Step 2 – Understand if your preferred substituted yarn is a match

The yarn band holds the key!

Next select your preferred choice of substituted yarn based on the information you get from the label (or online listing). You are looking for matches, or something as close to the pattern’s intended yarn (see step 1).

Don’t forget to also check for a dye-lot number, which means which batch of dye this yarn comes from. Yarns are dyed in batches and although recipes are followed, variations can and will happen across batches and you want to make sure with the retailer that you can get enough of the yarn dye lot as you will need to finish your project. If you can’t, then either choose another colour, or alternatively buy from two dye lots and knit alternate rows from each lot (this will give you a very slight striped effect depending on the colour, and yarn base). Knitting a gauge swatch will help you discover if this method works for you.

You will find independent dyers like myself typically dye in small batches, so make sure that if you want to choose this route that you explore options with the dyer. In my case most of my yarns are variegated, so batches aren’t an issue and you are expected to knit alternate skeins in alternate rows. Having said this, if you require enough of a colour for a larger project let me know and I will do my best to match skeins where possible.

Step 3 - Make a gauge swatch

Do I really need to swatch?

Gauge swatches are often skipped when we’re feeling keen to start a new project! However they are incredibly important, because they tell you a lot about the yarn you intend to knit with, in the drape, stretch and projected fit. A swatch also tells you how close you are to the original pattern and yarn choice.

Gauge swatching is crucial to a structured garment such as a close-fitting sweater, as you will want the garment to fit you properly when finished. For accessories a gauge swatch is not so vital as it is not intended to be a close fit to the body shape. However swatching is still advisable, because you will see how your yarn choice looks and feels in the stitch of your design.

You may decide to substitute a different yarn because your swatch is too rigid. You may decide to go up a needle size to open out the stitch pattern more. Or – hopefully – you may actually love the swatch and continue with your yarn choice.
Without the swatch you wouldn’t know this until partway through your project – and we all know how disheartening it is to pull a project back and have to restart it!

How do I swatch?

A traditional gauge swatch is knitted (or crocheted) flat in a square of 10cm, or 4 inches. However, if you intend to knit in the round, or have a larger design, such as a cable you may wish to knit a much larger swatch to see how one repeat of your pattern knits up and knit your swatch in the round if that is appropriate.

Check your swatch and see if this alternate yarn is a good match to the original.

If you have found a good match in your alternative yarn choice, then choosing the right needle size may also feel obvious. However, if you fall in love with a new yarn that is a slightly different weight, say sport weight, instead of 4ply, then you will need to test your gauge for the correct needle choice and sizing options, as a difference in weight will reflect heavily on how a garment knits up.

What do I do with the swatch?

If you’re not so happy with your swatch, decide what you’ll do to improve it. Do you need to knit another in a slightly larger or smaller needle size? Do you need to substitute a different type of yarn – for example a different fibre blend to improve structure for a garment?

If you do need to swatch again – do it! Yes it can be frustrating to feel like you’re stuck before you even start your new project, but I guarantee you’ll be much happier with the end result if you put in extra effort at this planning stage.

If you’re happy with your swatch, then yay well done! You can proceed with your project with confidence. If you need all the yarn for your project, just pull out the swatch and re-use it. If not, maybe you’d like to keep it in a folder with some project notes. Or even keep all your swatches and eventually use them to make a blanket reminding you of all your projects!

My top tips for substituting the advised knitting yarn in a pattern

I’ve substituted yarns in many projects with great success, but not every time.

Here are my top 2 tips to bear in mind when substituting the advised yarn in a pattern for your preference.

Tip One: It's all in the detail

Twice in garment projects (one sweater, one cardigan) I’ve had issues when substituting the specified knitting yarn on the pattern with one that I preferred. The tension, weight, etc was all fine, but during the knitting I found the different fibre made a huge difference.
The yarns I used were too heavy and drapey, so they didn’t give the structure that the garment needed. Whilst they looked great and fitted me, I never got to wear them because they just flopped and stretched as I tried them on. I knew my choice was off.

Remember – consider the properties of the recommended yarn not just the weight and tension, but also the fibre, structure and long-term wear.

Tip Two: All similar yarns are not equal

A common mistake I see knitters and crocheters make is substituting yarn based on the gram (or ounce) weight. Different fibres of the same weight (for example 4ply) can have very different lengths for an average of say, 100g. Let’s look at an example:

  • 100 grams (3.5 oz) of my Bright 4ply yarn (50% Merino, 50% Tencel) has approximately 333 metres (364 yards)
  • 100 grams (3.5oz) of my Sparkle 4ply yarn (75% Merino, 20% Nylon, 5% Gold Stellina Sparkle) has approximately 400 metres (436 yards)

That’s a quite a difference in length, and may give you a disappointing result if you don’t notice it!

Remember – consider the length of yarn you need to make the garment size you wish to wear.

There’s a lot to take in here, but it’s worth the effort. Go through the steps above when substituting yarns and you’ll have the best chance of loving your finished project.

Happy knitting!

Steph x

Knitting Yarn Guide: Types, Weights, and How to Choose the Right One
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