• Michelle

Yarn Substitution Mini-Series Part 3: Knitting Maths!

A teeny note ; ) This post is for those who like to approach things in a step by step manner and those who might be little trepidatious about knitting maths! Knitting Buccaneers* who like to get straight on in there may find all of this a bit sedate!

Speaking to people, and from my own experience, how you feel about maths depends a lot on how you were taught it in school. I had two great maths teachers, one in primary school and one in secondary school. So while I do not enjoy theoretical maths, I do like practical maths and the good news, is that knitting maths is practical maths. Knitting maths for me is like working out how much carpet you need to cover a floor!

My first tip for knitting maths, therefore, is, that if you are worried about maths, try to separate knitting maths from the incomprehensible things you learnt in school!


I sat the maths paper that contained this in 1999. I do not understand a single word in it now! My heart is actually racing just looking at it!

(Content copyright, Irish Department for Education)

Another teeny note: There is effort in doing this. If you want to essentially rewrite a pattern for a new yarn, you’ll have to put your back into it and do the maths. No one is judging you for not wanting to do that, there are millions of awesome patterns out there, but just to get that out there! I very rarely redo the maths in a pattern to reknit it and really only to introduce some extra shaping at the very very most. However there are folks who want to know and this post is mostly for them.


And one more note: A lot of the calculations are in inches only. This is to make it less cluttered. You would do the same in centimetres.

Start before you intend to begin

Even if you are not thinking about doing any adjustments to patterns, may I recommend looking at knitting patterns in a different way and try to understand what you are doing when you knit something in a way you haven’t before.

Now I know that that sounds really condescending but for a long time I just did was what I was told to do in the pattern. It was only when I needed (and I mean needed) to start writing patterns that I really looked at what was happening. Why has the designer done the decreasing in that way? What is this increase doing that another wouldn’t have done? Why is there this many repeats of the chart? How did they know I’d need to pick up that many stitches? Look at the different sizes and the proportions of each size together and individually. Understand why you might have more increases in one section for a smaller size than a larger size. Look at armhole depth, how armholes come together with armhole shaping. Once you start thinking about patterns in this way, rather than as just a set of instructions, it will help you when you approach patterns to make changes to them.

Now I am not suggesting that you don’t do this already or that you even need to but if you want to move on to altering patterns or even designing them, it’s a great first step.

If you are feeling adventurous, take patterns and drawn out the measurements that are missing based on what the pattern row and stitch counts are.

After all that though, my tip for your first major yarn substitution is to start small (see, definitely not a post for the extreme knitter!) Something where the shaping doesn’t matter is a useful start. This is an example of a basic stocking stitch scarf.


I am often asked why there are most increases in this section for the smaller sizes than for the larger sizes (those increases are in the next sizes). I am always happy to answer because we all only get better at knitting by asking :)

Basic stocking stitch scarf

Original gauge: 22 stitches and 28 rows to 4 inches / 10cm on 4mm needles

Scarf width: 8 inches / 20 cm

Scarf length: 70 inches / 180cm

New gauge: 28 stitches and 32 rows to 4 inches / 10cm on 3mm needles

To knit your scarf, all you’ll need is the number of stitches to cast.

Using the original gauge where 4 inches = 28 stitches, 1 inch equals 7 stitches so 8 inches is 56 stitches (8 inches multiplied by 7 stitches).

You now know that if you cast on 56 stitches your piece will be 8 inches wide.

For the length, it is much more straight forward in this example. A pattern in plain stocking stitch may say ‘Work in stocking stitch until the piece measures 70 inches’. In which case you would just continue knitting until the scarf was 70 inches, without needing to calculate the number of rows.

You will also notice here that the original gauge wasn’t required. Once you have the measurements, it is often possible to work out how many stitches and rows in the new gauge are required without using the old gauge.


A cowl is a good place to start when learning how to substitute yarn!

The process for re-engineering (as I see it, not scientific in any way!)

While the example above is very straightforward, it reveals the type of process that you need to go through to change from one gauge to another.

I think of the steps for re-engineering as follows:

1. Get the gauge of the yarn you want to use by knitting a swatch (rows/stitches per inch/cm)

2. Get the key measurements of what you want to knit from the pattern

3. Convert your key measurements into rows and stitches using your gauge

4. Work out the number of stitches you need to increase / decrease between stitch counts

5. Make sure that your stitch multiples work for any patterns/complex shaping etc

6. Check that the pieces that should match, will match

7. Write out your version of the pattern and knit it!

Get your yarn gauge

You will find all of the details above swatching in part 2 of this mini-series which is available here.

Get the key measurements

In many patterns you will get a set of measurements but these may not be all of the key measurements that you need to re-engineer the pattern. Using the pattern (and your own knowledge) you will need to work out which measurements you need and what they are in cm / inches. You calculate these using the pattern detail and the pattern gauge. We’ll look at two examples below.

Example 1: I am reworking a sweater that is worked flat. I have a cast on edge measurement and a bust measurement but I also need the waist measurement as I need to work out how much shaping I need to do. The waist measurement is not in the schematic.

To get your waist measurement, you will need to do the following:

1. Find the part of the pattern that relates to the waist of the sweater

2. Locate the number of stitches you have at that point

3. Divide the number of stitches by the number of stitches per cm/inch in the gauge

4. The number that results is the measurement of your waist. You can now calculate how many stitches you should have in your new yarn when you have completed the waist shaping

Waist stitch count (one side only): 160 stitches

Pattern Gauge: 10 stitches per inch

How wide is the waist?

160 divided by 10 = 16 inches

Your Gauge: 8 stitches per inch

New waist stitch count = 16 inches multiplied by 8 stitches per inch stitches = 128 stitches.

Example 2: The schematic gives me a measurement for the body length between the cast-on edge and the armhole shaping. However, there is a portion of shaping that needs to be done in part of the body but there is no measurement for that section on its own.

Often patterns have a note that says ‘Work straight until piece measures X cm / inches’. This is great because you don’t have to calculate the number of rows. However the shaping section of the pattern is as follows:

Increase row: Increase 1 stitch at each end of the row

Work an increase row and then work 5 rows in stocking stitch. Repeat these 6 rows a total of 10 times. (60 rows)

Shaping section row count: 60 rows

Pattern Gauge: 12 rows per inch

How long is the shaping?

60 divided by 12 = 5 inches

Your Gauge: 10 rows per inch

New shaping row count = 5 inches multiplied by 10 rows per inch = 50 rows.

So the key is to identify all of the key measurements in the pattern that you are converting and then convert them into the number of stitches and rows for your specific yarn.

To convert this sweater, you would need to get at least three more measurements before you started the conversion. Having changed this pattern from DK to 4ply, this is a relatively straightforward sweater to change.

Convert your key measurements into rows and stitches using your gauge

You’ll have seen in the examples above how you use the row and stitch counts from you gauge to calculate the rows and stitches that each measurement corresponds to. The trick here is knowing whether or not you have all of the measurements. A good way to do this is to check that for everywhere in the pattern where a stitch or row count is included, you have a new stitch or row count to update the pattern with.

Work out the number of stitches you need to increase / decrease between stitch counts

Once you have all of your key measurements, you will need to calculate the rates of increases or decreases in any of the relevant sections. I use Ysolda's magic formula for doing this and I highly recommend spending time watching her video on it. She explains it really clearer but also just gives you the formula if you don't have time to spend understanding finer points of it.

https://ysolda.com/blogs/journal/a-magic-formula-for-evenly-distributing-shaping

Make sure that your stitch multiples work for any patterns/complex shaping etc

In addition to calculating the stitch counts for different measurements, it is important to consider if you need a particular multiple of stitches. For example, if you want a 2 by 2 rib (k2, p2), you will need a multiple of 4 stitches. This is also a consideration for crown shaping in hats, stitch patterns and math other areas.

Check that pieces that should match, will match

Where you have pieces of work that will be sewn together or picked up and knit from one another, you need to ensure that the changes you have made to one piece corresponds to changes made to the other. This is particularly relevant for garments that are knit in pieces and then sewn together. Trickier items in this category would include set-in sleeves where you need to work out how the vertical edges of the back and front of the garment will fit with the horizontal edges of your sleeves.

Something to consider here is modifying not only the gauge of the pattern but some elements of the construction. It may be easier to pick up stitches around your armhole and knit your sleeve from the top down than to work out how to be certain your sleeve cap fits into the pattern.

Write out your version of the pattern and knit it …

Once you have all of your measurements, stitch and row counts, print the pattern, cross out all the details and insert your own. This is a great way of knowing if you have covered everything.

This may seem like a lot and it is! Until I started learning how to design, I knew there was a lot of effort that went into knitting patterns but I didn't know quite how much! However, if you have a burning desire for a particular pattern, the above will give you a starting point.

A note here: when you re-gauge a pattern, the design is still that of the designer so don't publish a version of the pattern, even a free one, without talking to the designer at the very least.

Calculating yarn requirements

One last thing before I close. I would be remiss if I didn’t talk about how to calculate the amount of yarn you need. I am by no means an expert on this (I'm about learning to walk but occasionally I fall over and bang my head!) but this is the general method many people use. It’s back to the practicality of working out how to know how much carpet you need for a room of a certain size. This is best explained with some examples!

Example 1: Cowl

My swatch is 6 inches by 6 inches (36 square inches (6 x 6)) and it weights 10g. My cowl is 48 inches in circumference and 12 inches high which is 576 square inches (48 x 12).

576 divided by 36 = 16

Which means that my cowl is 16 times the size of my swatch in terms of area. I therefore need 16 times the amount of yarn so 160g of yarn.

Example 2: Raglan Sleeve

This is very useful for regularly shaped items like rectangles and squares but what about something that is more irregular in shape, such as a sleeve?

Never let a lack of drawing skills stop you designing knitwear, I don't! ; )

In the picture above you will see a very badly drawn raglan sleeve. The blue line is the edge of the sleeve, the red lines represent a rectangle around the longest and widest part of the sleeves and the grey shading is where there is no knitting.

To get a rough idea of what yarn you need, you multiple the longest measurement (20 inches) by the widest measurement (8 inches). This gives you 160 square inches. Assuming the same swatch as above: 36 square inches and 10g of yarn, divide 160 by 36 and multiple by 10. You need 44g of yarn.

You are likely to have yarn leftover because the whole area isn’t covered in knitting. If you were designing with a view to publishing a pattern, the next step would be to knit a sample in one of the sizes and then workout how accurate the estimate was and make any adjustments along the size range.

You can also work out the area of the parts with no knitting and deduct them from the total yarn. I did this in Simply the Simplest sweater as there was a lot of unknit areas due to it being a batwing sleeve sweater.

Thank you for reading!

And that’s it! You now know the steps to go through if you want to substitute the yarn in a pattern. I didn’t say that it wouldn’t take a while but if you really want to knit something in a completely different yarn, doing the above will help get you there.


Thanks for reading. I would love to hear your thoughts on this and if there are any areas I can update to make them clearer! There is always something to learn in knitting and I definitely don’t know even a fraction of it! : )

Happy knitting (with or without yarn substitution!)

M.x


*Simon is replaying Black Flag at the moment, I can’t help the pirate references!


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