Yarn Math

Calculate How Much Yarn is Leftover

Trying to find out how much yarn you need for a project can sometimes feel like a guessing game. Do you have enough? There is one way to be sure. Do a little yarn math.

When you are finished with a project, you will often have leftover yarn; knitters call this “scrap yarn.” This leftover yarn can be perfect for smaller knitting patterns. Before you get started with a scrap knitting project, though, you will need to make sure you have enough yarn to finish it. With a bit of math, you will be able to calculate exactly what you have left. Learn how to do the quick yarn math or jump to the yarn length calculator at the bottom of this page.

Many knitting patterns are perfect for scrap yarn and pattern-writers will usually tell you exactly how much yarn you need. When an author provides you with the weight of yarn needed, calculating whether you will have enough is simple; just weigh your yarn and see if you have at least as much as the writer suggests.

Sometimes, however, a pattern-writer only lists a length of yarn needed. While this makes your calculations a bit trickier, you can do a little math to be sure you have enough yarn.

Tools Needed to Calculate Yarn Math

To find out how much yarn you have left, you will need two important items.

First, you will need the label from your yarn. Nearly every new ball of yarn you purchase will have a label noting yardage and weight. If you save the label, you will be able to calculate how much yarn you have left after a project.

You will also need a scale that weighs in ounces, so that you can measure the current weight of your yarn.

Basic Yarn Math Formula

To find out the yardage you have left after using some yarn, we will use simple ratios. A ratio compares two things; here we want to compare the length of our yarn to the weight of our yarn. Mathematically, you would write out our basic ratio like this:

But we are trying to find out the length of yarn we have now, based on information about the yarn we had when we had a full skein of yarn. So, we really want to compare two different ratios. If you can make the ratios equal to one another, you’ll have all the numbers you are looking for. Making two ratios equal in this way is called solving a proportion. Our basic math will start with this proportion:

If you’ve just finished a knitting project and you have your yarn label, you will have information to fill in three blanks in the proportion above. You will know the length of yarn in a full skein, the weight of yarn in a full skein, and the weight of the left-over yarn.

To calculate the length of your leftover yarn, you will “cross multiply, then divide.” This means, multiply the Length of Yarn in a Full Skein by the Weight of the Leftover Yarn (the two numbers you have across from each other), then divide that number by the Weight of a Full Skein of Yarn. The result will be the Length of Leftover Yarn.

Or just a bit more mathematically, use the following formula to solve:

An Example, Using the Yarn Math Formula

If you started with a ball of Caron Simply Soft Yarn, one of the suggested yarns in this book, the label would show that you started with 315 total yards or 6 total ounces of yarn.  After you’ve made a project or used some of your yarn, you weighed the leftovers to find that you have exactly 1.2 ounces of yarn left. How many yards is equal to 1.2 ounces of this yarn?

Start by filling in your formula with the numbers you know:

Then solve the math problem. Cross multiply (multiply the numbers shown in purple) then divide (by the number shown in teal). If it makes it easier, fill in the formula and solve:

Now, you’re ready to calculate how much yarn you have leftover. You can do the math yourself, or use the calculator below for quick answers.

Yarn Math Calculator:

Find Out How Much Yarn You Have After a Project

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