Yarn calculation

ricobonbonwOn my Too Many Pies blog I’ve talked about how I don’t like to follow patterns.

Now I’ve taken another technical step to develop my own knit patterns—calculating how much yarn I will need for a project before I begin, rather than jumping in and finding I don’t have enough yarn of a particular colour.

I’m knitting a cushion cover using Rico Creative Design Bonbon Super Chunky. (I’m a bit of a fan of self-striping yarn and this looks like it has a nice subtle gradation.) So, here’s my calculation:

Finished size of cushion cover, including double-sided and button down overlap:
35cm x 140cm (each side 60cm plus 20cm overlap)

Total area of knit fabric in cushion cover (A*):
4900 sq cm

Gauge swatch size using 7mm needles:
10 stitches = 10cm
12 rows = 10cm

Total area of gauge swatch (a*):
100 sq cm

Length of yarn in 100g ball (B*):
100 metres

Length of yarn in gauge swatch sample (b*):
5 metres

*Calculation for number of balls:
A ÷ a:     4900 ÷ 100 = 49
B ÷ b:     100 ÷ 5 = 20
49 x 5 = 245 (length of yarn required) OR
49 ÷ 20 = 2.45 (number of balls required)

Therefore:
The finished cushion cover size is 49 times bigger than the swatch size.
The length of yarn in the 100g ball is 20 times the length of yarn needed to knit the swatch.

Therefore I need approx. two and a half balls. That should be right, I think. I’ll let you know whether that works!

NOTE: The cushion cover is just a rectangle and conveniently the numbers above make for a pretty easy calculation. I look forward to doing more complex calculations in the future …

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