Knitting and crochet tension calculations made easy

Do the tension calculations for your knitting and crochet projects leave you feeling tense? Are you a designer wanting a little help to check sizing? Or are you wanting to tweak a pattern’s size, for example making a blanket larger or smaller than the sizes in the pattern? I’m going to take you through the calculations you might need to do, with some worked examples. I will also talk about when you might need to do each type of calculation. My examples will refer to crochet stitches, but the maths is the same for both crochet and knitting.

What is tension? And is it the same as gauge?

Before I begin, let’s clear that up. Gauge is a term more often used in patterns written in US terms, but for the purposes of this post I will use the word tension. However both mean the same thing-the number of stitches and rows over a given measurement. This is usually either 10cm x 10cm or 4 inches x 4 inches. You’ll often see these measurements given on the bands of yarn balls and at the start of crochet and knitting patterns.

I’m going to use cm, as it is my preference and also because the maths is easier to show. The tension triangles I’m going to share with you can be used with either cm or inches. The only thing I’d recommend is choosing either inches or cm for all of your crochet tension calculations. (If you are a designer who wants to use both in the pattern, work them all out in either inches or cm first. Then convert all of them to the other unit of measurement at the end!)

Why does tension matter?

If you want your item to be the same size as the pattern, tension is really important. For some things, like toys, it isn’t really critical. However, for garments it is very important to ensure a good fit. It is also useful for blankets so you know what size your finished items will be.

Knitting and crochet tension calculation triangles

These triangles will help you with the calculations you might need to do. From looking at each triangle, you can make 3 different tension calculations.

For stitches:

No. of stitches ÷ width = stitch factor

No of stitches ÷ stitch factor = width

Width x stitch factor = no. of stitches

For rows:

No. of rows ÷ length = row factor

No of rows ÷ row factor = length

Length x row factor = no. of rows

How do the tension calculation triangles work?

Let’s take stitch calculations first. You’ll often see the tension for a pattern written as, for example, 18 stitches x 12 rows = 10cm measured over dc using a 4mm hook. If we unpick that a little, it means that there are 18 stitches every 10cm and 12 rows every 10cm when working in double crochet using a 4mm hook. We can use that information to work out the stitch factor using the triangle.

18 (no. of stitches) ÷ 10cm (width) = 1.8

That means there are 1.8 stitches every cm, when working at that tension.

Now you know that, you can use it for other calculations.

Example 1: you want to make a blanket 75cm wide

Look back at the triangle – you have your stitch factor (1.8) and you know you want to make it 75cm wide. Width and stitch factor are at the bottom, with a x symbol between them. So you need to multiply them together.

75cm (width) x 1.8 (stitch factor) = 135

You need 135 stitches (if it doesn’t come out with a whole number, you can either round up or down).

Example 2: you want to know how wide a blanket will be with a given number of stitches

Look back at the triangle, you have your stitch factor (1.8) and you know how many stitches you have-for example 150. No. of stitches is at the top and stitch factor is at the bottom, with a ÷ symbol between them. So you need to divide the number of stitches by the stitch factor.

150 (no. of stitches) ÷ 1.8 (stitch factor) = 83.33cm

Your blanket will be approximately 83cm wide

Let’s move onto row tension calculations

We will begin by calculating the row factor, i.e. how many rows there are per cm. This is very important as it allows us to tweak the length of an item.

12 (no. of rows) ÷ 10cm (length) = 1.2

That means there are 1.2 rows every cm, when working at that tension.

Now you know that, you can use it for other calculations.

Example 1: you want to make a blanket 90cm long

Look back at the triangle – you have your row factor (1.2) and you know you want to make it 90cm long. Length and row factor are at the bottom, with a x symbol between them. So you need to multiply them together.

90cm (length) x 1.2 (row factor) = 108

You need 108 stitches (again, if it doesn’t come out with a whole number, you can either round up or down).

Example 2: you want to know how long a blanket will be with a given number of rows (this is especially useful if you are wanting to add on chunks of pattern repeats)

Look back at the triangle, you have your row factor (1.2) and you know how many rows you have-for example 125. No. of rows is at the top and row factor is at the bottom, with a ÷ symbol between them. So you need to divide the number of rows by the row factor.

125 (no. of rows) ÷ 1.2 (row factor) = 104.16cm

Your blanket will be approximately 104cm long.

Tension issues

What happens if you make a tension swatch at the start of a project and your stitch and/or row counts aren’t the same as the pattern?

First of all change hook or needle size-go up a size if you have too many stitches or rows per 10cm or down a size if you have too few.

If you can’t get both stitches and rows to match the pattern, it is sometimes possible to adapt the pattern slightly. For example, if you can get the numbers of stitches to match the pattern tension, you could adjust the number of rows. Often, a pattern will state ‘work until it measures xcm’ in which case that is quite easy. You will need to be careful though if you have shaping involved, for example for armholes, to ensure you don’t end up with the armhole too large or small. It is best if you can get your tension to match that of the pattern in this case, otherwise you may end up having to do a lot more complicated maths.

I hope you’ve found this guide to knitting and crochet tension calculations helpful, if you have any questions please add them in comments and I’ll try to help you out! If you’re a designer wanting support with a crochet pattern, you can find out more about my tech editing services here.