Yarn substitution is really easy once you're familiar with the process.  Firstly, what is yarn substitution?  Basically, it's substituting yarn that has been used in a pattern for another yarn.  For example, you might be planning to knit a pattern that calls for a specific yarn, but the yarn listed has been discontinued; or, you might want to use some of your own yarn that you've been eyeing off in your stash.  I remember when I first started knitting that I found this to be rather daunting, but over time I learned a few helpful tips that made yarn substitution a breeze.  I'm going to share these tips with you, and I'll be using the Portage cardigan pattern (by Melissa Schaschwary) that I recently knit to demonstrate how.

Locate the yarn information in the pattern

Every knitting pattern includes a description of the yarn that was used to knit the original design. Sometimes you might want to check which yarn was used before you commit to buying the pattern.  All the information you need can be found for free on the Ravelry pattern page.  When looking on Ravelry, you will  find this information to the right of the pattern page (see below).

This is pretty much the only information you will need to substitute yarn successfully.  The only time you need to know more is if a novelty yarn or a highly textured yarn has been used as they will effect the overall appearance and gauge of your final piece.  In these cases, it is best to match yarn texture (e.g. fun fur and boucle) as well as considering the following points.

Yardage

Comparing the metres or yards (i.e. the yardage) of the yarn used in the pattern to the yarn you wish to use, is one of the most important steps in substituting yarn.  In our example, the yarn listed on the Ravelry pattern page (see above) has a yardage of 227 metres in 100g.  I substituted this yarn for our Voyage DK, the label of which reads:

Our yarn is 210 metres in 100 grams, which is 17 metres less than the yarn that is called for in the pattern.  I normally allow around 20 metres difference (plus or minus) between yarns, so this one is a good match.  Basically, you need match or get close to the yardage of the yarn used in the pattern, for this will mean that your yarn thickness or weight will be similar and hence so will your gauge.  More on that later!

So, what happens if the two types of yarns have different weights per skein or ball?  For example,  the skein that you have is 115g but the yarn in the pattern weighs 100g?  What you need to do here is is to convert your 115g into 100g.  It sounds complicated, but it is really easy.  Here's how you do it.

Say the yarn we want to use is 280 metres / 306 yards in 115g BUT the yarn used in the pattern is 227 metres / 248 yards in 100g. Use the formula:

metres (or yards) per skein / grams per skein x grams needed

280 metres / 115g x 100g = 243 metres in 100g

We are wanting something close to the yardage of the yarn listed in the pattern: 227 metres in 100g.  Using the formula the yarn that we want to substitute works out to be 243 metres in 100g, which is 16 metres more than the yarn listed in the pattern.  Given that we can use yarn that is plus or minus 20 metres, our yarn looks to be a good fit!

Please don't rely on matching yarns using the allocated weight classification, and by that I mean matching a 'DK' to a 'DK' weight yarn.  A yarn company can add its own classification to a yarn label, which means that a yarn that has been classified as a 'DK' might actually be more similar to a Sport.  The only foolproof way to successfully substitute a yarn is by comparing yardages.  Also, be careful that you don't mix up metres and yards!  Make sure you are comparing metres to metres or yards to yards - don't mix them up!  And, of course, play close attention to the weight of each yarn. Like I have said yarn can come in 50g, 100g, 115g, 150g etc. skeins or balls, so make sure you are comparing the same weight of yarn per yardage. If needed, use the formula above to convert the yardage so that each skein is equal in weight.

Fibre Content

In our example, the yarn used for the design is a mix of 70% merino, 20% alpaca, and 10% silk.  I used a 100% merino and it worked well.  My general rule of thumb is to match the yarn blend as closely as I can.  I could have also used a merino and alpaca blend or a merino and silk blend, as long as the merino content was around 70%.  When I started knitting this really used to throw me.  I thought that I had to precisely match the yarn blends to the exact percent!  Please don't let these percentages scare you; close enough is usually good enough. 

Matching fibre types as closely as possible is important because different types of fibre do affect drape and structure of the finished piece.  Yarns that contain silk do drape differently than, say, cotton.  Cotton and linen yarns have quite a bit of structure when knitted up so substituting these yarns with merino or alpaca will dramatically effect the finished shape.  Basically, look for yarns that have similar fibre types.

What about superwash and non-superwash yarns, do they differ and should this be a consideration when substituting yarns?  You can substitute a non-superwash yarn for a superwash yarn (and vice versa); however, keep in mind that superwash yarns do tend to stretch more after washing than non-superwash yarns.  So this is more an issue that relates to gauge (see below).  Also, think about who you are knitting for: is this project for you or are you giving this to a non-knitter who may not know how to care for hand-knitted items?  Generally substituting a non-superwash yarn for a superwash yarn (and vice versa) is totally fine.

Checking the amount of yarn needed

When substituting yarn, how do you know how many skeins you'll need?  OK, I get asked all the time: 'how many skeins of yarn will I need for such and such pattern'?  Firstly, you need to check the pattern to see how much the total yardage was for the design in your size.

Using our example, I knit size 35.  The total yardage for this size is listed as 1850 yards or 1700 metres.  The yardage listed on the Voyage DK yarn label (see above) is 230 yards / 210 metres. Here is the formula you would use:

Total pattern yardage / total yardage per skein = number of skeins needed

So calculating in metres you divide 1700 metres / 210 metres = 8.095 skeins.  I would round this up to 9 skeins just to make sure I had enough yarn.  You can also calculate this in yards which would be 1850 / 230 = 8.043 skeins.  So, again around 9 skeins just to be sure.  Just remember that for the formula to work you need to work in either metres or yards.  Otherwise you may be playing yarn chicken - yikes!

Gauge Swatch

Gauge swatches are critical for knitting a garment that fits, but that is a whole other blog post!  In regard to yarn substitution, your gauge swatch is a great indicator of how your yarn knits up.  Does the fabric look good when knitted at the recommended gauge?  Does the fabric have the right feel for you?  Is the yarn showing off the stitch pattern nicely?  These questions are all answered with the gauge swatch, so don't skip this step!  You might knit the gauge swatch and find that the yarn isn't working out how you imagined, which means looking around for another one to use.  It's much better finding this out on a small gauge swatch than after days of knitting on a larger project.

Still unsure?  Then check out these sites

Sometimes we just need a little more reassurance before we dive in to substituting yarn.  Here are a list of online resources that can help make your decision easier:

• Yarn Sub - this is an online yarn database that will actually search for yarn substitutions for you.  Just type in the yarn that you want to substitute and it will give you a list of similar yarns.  The only drawback is not every yarn brand (especially indie dyed companies) are listed, but the major ones are.
• Ravelry pattern pages - these are a wealth of information.  You can actually click on the  'Yarn Ideas' tab at the top of the page to see what yarns other knitters have used.  Most of the yarns used by Ravelers have been substituted.  You can also click on the link under each yarn to see what the project looks like in that yarn.  It's such a great resource, so don't forget to use it!.
• If you are unsure if a yarn will work for a specific pattern, just ask.  Post a question on Ravelry, email the yarn company or indie dyer, or ask at your LYS.