How to Estimate the Amount of Warp Yarn for Any Weaving Project

Have your heart set on a weaving project? You’ll want to know how to estimate the amount of warp you will need! Just like weft, the amount of warp you need depends on things like the width and length of your fabric, the sett of your warp and weft, the type and weight of your yarn, and the weave structure you are using.

Using some of the same ideas we covered with weft yarn, let’s look at how to work out the amount of warp yarn we’ll need for our weaving project, using some simple formulas.

Calculating Warp Length

Regardless of whether it is for warp or weft, yarn is typically sold by weight, such as 100-gram skeins, 250-gram spools, or 1-kg cones. To figure out how much warp yarn we need, the first step is to figure out the length of yarn (yardage) we will use. To do this, we need to know:

• The length of our fabric, in inches or centimetres
• The width of our fabric, in inches or centimetres
• The sett, or ends per inch (EPI), of our warp
• The sett, or picks per inch (PPI), of our weft
• The percentage of shrinkage and take-up of our yarn

Step One: Working in Two Dimensions

First up, we know the length of the fabric on the loom—we can use this as our initial guess of how much warp yarn we use for the fabric itself.

Next, the warp sett tells us how many ends we will need to dress the loom with to make a unit width of fabric. This is usually an inch of fabric for imperial measurements and a centimetre of fabric for metric measurements. So, if we multiply the length of the fabric by the warp sett, we get a number for how much warp yarn we need to produce a unit width of fabric.

And finally, we have the width of the fabric we want to weave. If we multiply the amount of warp yarn we need to produce a unit width of fabric by the total width of fabric, we have an estimate of the warp yarn we need to weave that fabric.

As a formula:
Approx. Total Length of Warp = Length of the Fabric x Warp Sett x Width of the Fabric

Step Two: Refining our Warp Estimate for the Real World

Even though we now have some idea of how much warp yarn we need, there are still some elements we need to cover. In this step, let’s take deal with the fact that our fabric isn’t two-dimensional—it is three-dimensional.

As we weave, the path the warp takes isn’t perfectly flat and straight—especially after we cut the fabric off the loom and wet-finish it. Just like when we calculated the weft yarn amounts, both the take-up and the shrinkage­ are affected by different yarns and yarn structures, so it pays to sample and get a percentage allowance for shrinkage and take-up that you can feel confident about.

(Want to skip the sampling? For balanced weaves and square setts, many weavers add a 10-15% allowance as an average shrinkage and take-up factor in both the warp and the weft).

Use the shrinkage and take-up factor to refine our warp yarn estimate. So, for example, if need to add 10% for our shrinkage and take-up allowance, we can multiply our Step One estimate by 1.1 to get our new and refined estimate for the length of weft yarn we need for our project.

Step Three: Loom Waste

So far, we have taken the same steps as if we were calculating weft yarn length. Familiar, yes? What we have calculated so far is only covering the yarn that goes into weaving the fabric. We also have to account for the extra yarn we need to get the loom working—at the start and the end of the warp.

All looms can only weave until a certain point from the end of the warp. At some point the back apron rod will get too close to the heddles and either prevent you from advancing the warp further or from making a clean shed. That means that we need extra warp length to cover the distance between where the apron rod is when we finish weaving and the fell line (i.e., our last pick of weft). The exact amount will be different for different looms and so you will get to know yours, but most published patterns will let you know what they have calculated for so that you can accommodate your needs.

(One advantage of a rigid heddle or table loom is that there is less loom waste!)

The final part of the loom waste is what it takes for us to attach the warp to the loom. Again, different methods, such as lashing on and tying on, use different amounts of yarn.

Once we know how long the loom waste is for one end, we can use the sett to figure out how much in total we need to accommodate the loom.

Summary: Formula for Calculating Warp Yarn Length

Total Length of the Warp
= (Width of the Fabric x Warp Sett x Length of the Fabric x Shrinkage & Take-up Factor)
+ (Loom Waste Per End x Warp Sett x Width of Fabric)

Now that we have a formula, we can see why we can make some quick back-of-the-envelope guesses for these values when our projects meet certain conditions. For a project using a balanced weave, square sett, and the same yarn in warp and weft, we have a project where the warp sett and the weft sett are the same. We also have the shrinkage and take-up factor the same for both warp and weft. In these circumstances, the amount of warp in a piece of fabric (not including loom waste) is equal to the amount of weft in a piece of fabric.

Sometimes you see the calculations completed in a way that is slightly easier to accomplish mathematically but ends up including the shrinkage and take-up factor on the loom waste. It usually only results in a slightly higher amount of loom waste and is a perfectly fine solution! In practice, everything being equal, you might just end up with a little bit more warp for sampling and play

When you estimate warp, don’t forget to include enough fabric length for sampling.
If you are going to go to all that effort to dress a loom, you might as make the most of it!

Calculating Warp Weight

We now know how long our warp yarn will be, so we can calculate how much it will weigh. To do this, we need to know:

• The total length of weft in yards or metres
• The count or weight of your weft yarn (a.k.a. linear density or grist)

How to calculate warp weight depends on what type of count your yarn uses. We break this down in our article on weft yarn calculations, with an example, so I encourage you to check it out if you want a refresher.

Tips and Resources for Weaving Calculations

• Felicia Lo has included a Google Sheets file for you in the Double-Weave on 4 Shafts course at the School of SweetGeorgia. Using a weaving calculator tool makes these repetitive calculations easy peasy! I like ones, like spreadsheets, where I can look at the formula and see how it works.
• To measure the WPI, EPI, and PPI of your yarn and fabric, use a ruler, a tape measure, or a special gauge. You can also calculate WPI for your yarn if you want more math!
• Don’t forget to include enough fabric length for sampling. If you are going to go to all that effort to dress a loom, you might as make the most of it!
• Weaving books are great for little bits of information, like tables of conversions for yarn counts. For some common ones, check out Laura Fry’s article about yarn count.

Happy weaving!

Original publication: October 12th, 2023; Refreshed: February 11th, 2025 

The post How to Estimate the Amount of Warp Yarn for Any Weaving Project appeared first on SweetGeorgia Yarns.