Math Monday: Calculating Yards per Gram

Last week I wrote about the mystery yarn I picked up from Harrisville Designs at Rhinebeck - the one without a name or a label to list yardage or weight.

Maybe you have some yarn in your stash that doesn’t have a label or a partial skein that you knitted long ago, but you have no idea what it is. This week, I’m going to show you how to use simple measuring and math to calculate how much yardage is in my mystery yarn. You can try it with your stash mysteries too!

You’ll need 3 things: a rigid ruler, a scale that measures grams and a calculator - your phone calculator will do nicely.

Step 1: Weigh your skein or cake. In this picture, you can see that the cake’s weight is 113 grams.

Step 2: This ruler is 1 foot long. A yard is 3 feet long. I wrapped the yarn (without pulling too tightly) around the ruler 9 times. 9 feet of yarn divided by 3 feet per yard = 3 yards. So I have 3 yards of yarn.

Step 3: Weigh 3 yards of yarn you measured out. You can see that the 3 yards weighs 2 grams.

Step 4: Now the math part. We’ll set up a ratio. Don’t be scared. You did this in 8th grade.

x is the unknown yardage of the cake. We know the cake weighs 113g. So on one side of the equation we write x over 113. We also know that 3 yards of yarn weigh 2g. On the other side of the equation we write 3 over 2. When you do this, be sure that your yardage is on top and your weights are on the bottom on both sides of the equation.

Now cross multiply: x multiplied by 2 on one side of the equation (2x) and 113 multiplied by 3 (339) on the other side of the equation.

Now solve for x. You might remember that what you do to one side of the equation, you must do to the other side of the equation. So divide both sides by 2: 2x divided by 2 equals x; 339 divided by 2 equals 169.5.

And there you have it. You’ve calculated your yardage!!! This means that 113g of this yarn has 169.5 yards in a cake of 113g.

Of course, each skein varies a little in weight. I can use my calculated yardage per skein as an estimate or, if I want a more accurate accounting of how much yarn I have, I can weigh each skein and calculate more precisely by substituting the weight of each skein for 113g in the example above.

Give it a try and let me know how it goes.