Have you ever gotten 2 sleeves away from finishing that sweater, only to discover that you don't have enough yarn? Have you made late night phone calls to your LYS looking for a dye lot that they sold out of yonks ago?
While the current projects cannot be helped, there is still a way to prevent future heartbreak. It does require that you knit a swatch, though, so be warned.
You will need:
-a scale that can measure to within tenths of a gram (or pound)
-a ball of your chosen yarn
-a line counter/ yardage counter
To begin, wind your ball into a center pull ball while using your yardage counter. After you have wound your ball into a center pull ball, make note of the yardage measured and then weight it. I have found that MOST of the time, the weight on the ball band is not, in fact, the weight of the actual ball. This gives you the ratio you need to determine your yardage needed.
Let's say that Yarn Q weighed in at 1.2 grams and that the yardage measured for the ball was 65 yds. Divide the yardage by the number of grams and you get the ratio that is necessary. Yarn Q's yardage per gram is 54.166 yards per gram, or 65/1.2. Also check the ball band to see what they say is the approximate yardage. In Yarn Q's case. it says that there is approximately 60 yards per ball.
When you do your swatch in the pattern, measure the weight of the ball again after you have detached your swatch. Let's say that the ball now weighs .99 grams. This means that you used .3 grams of the ball knitting that swatch. To determine how many yards you used to knit your swatch, you simply use the yardage per gram that you determined before, and plug it into this formula:
Yards X
------------ * ----------------------------
Gram grams used in swatch
Where X equals the number of yards used in swatch
54.166 X
----------- * ------------
1 .3
X= 16.2498
For those of you who remember algebra, you need to multiply the known yards by the grams used, then divide by 1 (the number of grams in the ratio)
In our example, this would be 54.166/1 times X/.3 which, we multiply known yards 54.166 by the grams used .3 (which equals 16.2498) and then divide that number by 1, and you get that you used 16.2498 yards of your ball to knit that swatch.
Go back and look at the pattern. How many square inches are required for each side of your sweater? And how many square inches were in your swatch? Let's say that the swatch was 5 inches by 5 inches, or 25 square inches total. If the sweater pattern has the schematics that tell you the length and width of the pattern, and the front and back are both equal, you can simply multiply the length and width to get the total square inches, and then multiply by 2 to get the square inches needed for both front and back. Then do the same thing for the sleeves. Let's say that the height of the sweater is 27 inches, and that the width at the widest point is 17 inches. That means one side of our sweater requires 459 square inches, so the front and back together would require 918 square inches of fabric. And that the sleeves were 15 inches long, and 7 inches wide. For two sleeves, it requires [15 * 7 * 2] or 210 square inches total.
So far, we figured out that our swatch was 25 square inches and took 16.2498 yards to knit, and the sweater itself requires 1128 square inches {918+210) of fabric. All we need to do is some more algebra to determine the total y ardage. Multiply the sweater square inches by the swatch yardage used, and then divide by the swatch inches. This tells you that you need 733.19 yards in order to knit the 1128 square inches for your sweater.
Now go back at look at the yardage per gram ratio. This is the last bit of math you'll need to do. Divide the total number of yards required for your sweater by the number of yards per gram. This tells you that you will need at least 13.536 grams of your yarn in order to knit up that sweater.
Swatch inches Sweater inches
---------------- * -------------------
Swatch yards Y
Where Y equals the yardage required for the sweater
25 1128
---------- * --------------
16.2498 Y
Y=733.19
Simply go back and look at your ball bands, and then you can figure out the number of balls needed. The chosen yarn said that there was approximately 60 yards per ball, and we needed 733.19 yards total, so that means we need about 12 balls of yarn. Congratulations, you have just determined the number of yards needed and also the number of balls needed for your pattern.
Now as you knit, you know all the weights needed to finish each part of the sweater, so when you get to the sleeves, you can simply weight the yarn you have left to determine if there is enough, and then knit merrily away, knowing you are safe.
Of course, due to the possibility that the gauge goddesses will try to mess with you, always buy one extra ball of your yarn, in the same dye lot, just to be safe...
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