how much more yarn will I need?

Like quite a few of you, I’ve been knitting a Carbeth jumper. This one is my fourth, and each iteration has been, in its own way, an experiment. I made the body of number 4 even more cropped than in the pattern (the length from hem to underarm here is just 6.5 inches) and tried knitting, for the first time, with two different shades of Buachaille held together. I used Haar and Squall – two natural shades of grey which unite into a deliciously humbug-y marl.

One obvious question many knitters have, when altering the length of this garment from what the pattern specifies, is how much more (or less) yarn will be required. If you want to knit the body of your Carbeth longer or shorter than the pattern recommends, here’s how to figure that out.

Lets say you are knitting the second size of Carbeth and want to knit the jumper 8 inches longer. To understand how much yarn you’ll need you have to figure out two things:

A: The number of extra stitches you’ll be knitting to reach your desired body length and
B: The weight of yarn (in grams) per stitch.

Contrary to what you might think, neither of these things are difficult to ascertain.

To calculate A (the number of extra stitches required for your added length), you must first work out the total number of extra rounds you need to knit. To do this, simply multiply the pattern’s row gauge by your desired extra length.

In our example, you want to add 8 inches to your Carbeth jumper, so you’ll multiply these 8 inches by 5 rows per inch:
8 inches x 5 rows per inch = 40 rows.

Now you need to multiply the number of extra rows by the number of cast-on body stitches (as the body is worked straight to the underarms we don’t have to worry about shaping). In our second-size example, you’ll have cast on 140 stitches.

140 body stitches x 40 extra rounds = 5600 stitches – so:
5600 = the total number of extra stitches you need to knit to add 8 inches of length to your jumper.

To figure out B (the weight of yarn used per stitch) you need a swatch which has been knitted exactly to the gauge specified in the pattern.

To swatch:
Cast on 50 stitches and knit in the round for 20 rounds. (It’s important to work the swatch in the round because you want it to be knitted in exactly the same way as you will later knit your jumper).
Bind off and block your swatch.
You’ve now worked 1000 stitches, plus the cast on and bind off rows.
Block your swatch. If the swatch is not coming out at the specified pattern gauge (14 stitches and 20 rows to 4 inches), start again, increasing or reducing your needle size accordingly.

Once you’ve got your thousand stitch swatch that is knitted to gauge, weigh it.

My swatch (above) weighs 26g, that’s 1000 stitches, plus two yarn tails, plus the yarn used for the cast on and bind off rows. To exclude the cast on and bind off from the calculation, I’m going to round the weight down to 25g, which is a nice number to work with.

We now know now that 1000 stitches knit to gauge weighs 25g.

And to figure out the weight of a single stitch, we can simply divide the total weight of the swatch by 1000 – so: 25g / 1000 = 0.025g.

a single stitch weighs 0.025g

That’s right: 0.025g! And this scintillating revelation will allow you to calculate how much more yarn you will need.

To arrive at the final weight of extra yarn needed to add 8 inches to your jumper, simply multiply the total number of stitches calculated in part A by the weight per stitch calculated in part B.

In our example, 5600 (extra stitches) x 0.025 (grams per stitch) = 140g

That’s it! You’ll need a extra 140g of yarn to add 8 inches to your jumper. If you are working with Buachaille held double, like me, that’s another 3 x 50g skeins, or if you are working with a standard bulky weight, you’ll need an extra 2 x 100g skeins. If you were being careful, you might also want to add a 10% contingency to your 140g figure to accommodate small gauge differences which may occur when knitting, or disparities in the length & weight of individual skeins of yarn.

I hope this has been helpful and that you (like me) are enjoying knitting this jumper. I’m going to have a go at making a Carbeth cardigan next. Watch this space!