13 November 2006

Doily math, part 3

No, no, don't run away! This math stuff comes in handy, I swear!

Laritza asked how much thread I used for Weintrauben. This pattern wasn't that big—it was 130 rounds. I used only one ball of Cebelia 30, which is about 560 yards per ball. I had a small amount left over, enough that I was never nervous about running out at the end, but I doubt I would tempt fate and start a 140-round pattern with only one ball on hand.

Now I have a personal benchmark for knitting with Cebelia 30. According to all that stuff that got worked out in Doily Math Part 1 and Part 2, it should take four times as much thread to knit a pattern with twice the number of rounds.

Whoa, whoa, slow down. Where did that come from?

Hmmm. There's a reason why I'm not a math teacher. Let me see if I can just boil it down to an easy-to-use general formula.

Let's say you know how many rounds you can knit with one ball of some thread before running out. (I strongly suggest subtracting say, 4 or 5 rounds from this number, just to give yourself some room for error and because you will need extra thread to crochet off the doily at the end.)

  • The estimated number of rounds you will be able to knit =

    √(number of balls you have * (the number of rounds you can knit with one ball)²)
In case the math symbols are hard to read: square the number of rounds you can knit with one ball, then multiply that result by the number of balls, then take the square root of the whole thing. That's how many rounds you can get out of the balls of thread you have.

Note that the above formula works with fractions of balls too (i.e., number of balls you have can equal .5 or 1.5 or whatever). If I can knit one 130-round pattern with one ball of Cebelia 30, according to the formula, I should be able to knit one 90-round doily out of half of one ball. (Since I'd never know if I have exactly half of a ball, what this really means is that I can get two 90-round doilies out of one new ball.)

Ok, I'm done with boring math stuff for now. Knit on!